This article is no longer being updated. For the latest, click here.

Tropical Storm Harvey's multi-day siege on Texas and the Gulf Coast has killed at least five, prompted thousands of rescues and triggered catastrophic flooding across the Houston metro. Now, swollen waterways are prompting evacuations in surrounding areas.

New mandatory and voluntary evacuations were ordered in Fort Bend County, Texas, southwest of downtown Houston, over fears and expectations that water levels in the Brazos River will reach record levels, threatening to overtop local levees and inundate homes and businesses.

"A 59-foot river level threatens to overtop many of the levees in our area," said Fort Bend County Judge Robert Hebert. "If you are in a mandatory evacuation zone, please leave. If you do not, you may be in danger and we may not be able to help."

(MORE: Why Houston Didn't Order Evacuations)

More evacuations could come with record-breaking flooding bursting the banks of waterways further downstream. Five waterways have already crested to their highest levels ever, according to weather.com senior meteorologist Jon Erdman, and five more, including the Brazos River, are forecast to crest above their all-time record.

"The heaviest rain early Monday morning extended from near Beaumont/Port Arthur, Texas, into far southwestern Louisiana, with radar rain rates estimated over 4 inches per hour over in some spots," said Erdman. "Rain is still falling over parts of the Houston metro area, mainly in Fort Bend and southern Harris Counties, but is much less intense than we saw during the weekend."

Texas Gov. Greg Abbott has activated 3,000 national and state guard members after Harvey dumped more than two feet of rain on Houston metro, causing historic flooding from rainfall that has been characterized by the National Weather Service as "beyond anything experienced before."

A voluntary evacuation was posted for residents in Inverness Forest Subdivision north of Whitestone Lane, including east and west Greenbrook Drive and Kenchester Drive. Cypress Creek near I-45 could top the levee by Monday morning, according to the Harris County Flood Control District.

"There is life-threatening, catastrophic flooding happening now in Southeast Harris County," Jeff Lindner of the Harris County Flood Control District told The Weather Channel.

Two people have died in the Houston area in flood-related deaths as torrential rain continues to fall, according to the National Weather Service.

The Harris County medical examiner's office confirmed a woman was killed in flooding Saturday, according to AP. She appeared to have exited her vehicle in high water and was found 30 yards away by neighbors. The Houston Fire Department said a man died in floodwaters overnight Saturday into Sunday.  Two people reportedly died in Galveston County Sunday.

(MORE: President Trump Unleashes Harvey Tweet Storm)

Dr. Greg Postel, meteorologist and hurricane specialist for The Weather Channel, said the flooding unfolding in the Houston area "could be the worst flooding disaster in U.S. history;" and Gov. Abbott, appearing on Fox News Sunday, said: "We're measuring rain these days not in inches but in feet."

In an on-air phone interview with The Weather Channel Sunday, Texas Senator Ted Cruz said the number 1 challenge for emergency officials right now is securing more assets for high water rescues.

He added that he spoke with Gov. Abbott, who says they have 60 boats, 20 helicopters, 600 troopers and 3000 National Guard soldiers mobilized to help rescue people. 

In addition to the rescue crews, Cruz said residents with flat-bottomed boats have been assisting with saving people from flooded homes. He thanked Texas residents and those pitching in from other states, describing the outpouring of help as "inspirational" and a reminder that "there's a lot more that unites us." 

Despite the outpouring of help, Cruz says this is an active crisis situation and the need for rescue assets will only continue to grow. 

Sunday President Donald Trump tweeted that he would visit Texas "as soon as that trip can be made without causing disruption," the Associated Press reported. The White House later announced that the trip would be made Tuesday. 

Officials in Dallas are preparing the Kay Bailey Hutchinson Convention Center to become a "mega shelter" for Harvey evacuees, CBS DFW reports. Office of Emergency Management Director Rocky Vaz said they hope to take in evacuees by Tuesday morning.

“We have been advised by the state to be prepared for up to 5,000 evacuees, and we are committed to doing whatever it takes to accommodate our fellow Texans who may need assistance,” said Vaz. 

Houston Mayor Sylvester Turner said that as of 5 p.m. local time Sunday, the city received nearly 6,000 calls for rescues and that more than 1,000 have been rescued, AP reports. 

He urged people to "remain calm, remain patient." He noted that most thoroughfares are impassable and said he's ordered neighborhoods to open libraries and multi-service centers to offer "lily pad" safe havens for people who cannot flee the city because of flooded roads.

"I don't care if there is no food or water there, I just need to have a safe place for people to go," he said.

Gov. Abbott says 18 counties are now covered by a disaster declaration approved by President Donald Trump, according to AP. Almost 7 million people live within those counties, out of Texas' overall population of 27.8 million.

(MORE: The Latest Forecast for Hurricane Harvey)

Sunday the U.S. Army Corps of Engineers announced it plans to begin releasing water into Buffalo Bayou from the Barker and Addicks reservoirs on the western outskirts of Houston, according to AP. Col. Lars Zetterstorm said water will be very slowly released from the dams Monday morning to prevent uncontrollable flooding in downtown Houston and the Houston Ship Channel. 

He described the water contained by the dams as "unparalleled in the dams' history." The waters are rising by roughly 4 inches every hour.

When reporters asked why no evacuations were ordered despite days of warnings from the National Weather Service, Turner said it would have been "too dangerous" to have millions of residents on the road, noting that "if you think the situation right now is bad and you give an order to evacuate, you are creating a nightmare."

"The best place is for people to remain in their homes," he said.

The mayor and Harris County Sheriff Ed Gonzalez urged people to only use 911 in dire emergencies, noting that dispatchers were struggling to keep up with the calls."Difficult to get to everyone right away," Gonzalez tweeted. "Hang tight."

The National Weather Service is warning people to seek shelter on their roofs rather than in attics to avoid becoming trapped by rushing water.

The runway at Houston's Hobby Airport was completely flooded Sunday, according to a tweet from the airport. Officials closed the airport Sunday morning due to the storm, and it will remain closed until at least Wednesday. The George Bush Intercontinental Airport is also closed until further notice.

U.S. Coast Guard Air Station Houston says it has five MH-65 Dolphin Helicopters conducting rescues in the greater Houston area and is requesting additional HH-60 Jayhawk Helicopters from New Orleans and support from the Air National Guard to support rescue efforts.

Coast Guard Capt. Kevin Oditt said Sunday afternoon that helicopters have rescued more than 100 people in the Houston area.

The Houston Chronicle noted that some highways were so deluged, water lapped at overhead signs. The Harris County Sheriff's Office says some homes have taken on more than 6 feet of water.

Parts of southeast Houston received 12-19 inches of rain in just six hours Saturday night into early Sunday, according to the Houston Flood Control District.

Buffalo and Brays Bayou on the west side of The Loop are climbing out of their banks due to torrential rainfall. In addition, Mary's Creek in Friendswood has surged out its banks, surpassing its 500-year water mark.

Staff at Houston television station KHOU-TV were broadcasting live coverage of the floods when floodwater from nearby Buffalo Bayou began to enter the building.  The anchors and news operations at the station moved first to a second floor before finally abandoning the station.

About 15 seniors were evacuated from La Vita Bella nursing home in Dickinson, Texas, Sunday after Timothy McIntosh tweeted a dramatic photo from the nursing home owned by his mother-in-law.

The photo was captured by his mother-in-law. McIntosh told the Galveston News he hoped the viral tweet would convince the National Guard to help out and it did.

The Houston Independent School District said that all schools and offices will be closed for the week due to Harvey, according to a release.

Because of the storm, four cruise ships due this weekend to Galveston with a combined 20,000 people on board will wait until Tuesday to return to port, WFAA reported.

Rep. Sheila Jackson Lee, D-Houston, called on the White House and the Department of Homeland Security to "immediately declare Harris County as a federal disaster area," noting that damages in the county have already exceeded the federal threshold of $14 million, the Houston Chronicle reports.

Rockport Shredded

A Rockport man was killed when his house caught fire at the height of the storm, according to media reports.

Buildings were ripped to shreds in Rockport and firefighters were unable to respond to pleas for help in the hours following Harvey's Friday night landfall along the Texas coast.

In Rockport, a town of about 10,000 located on Aransas Bay, KTRK-TV reported 10 people sustained injuries when the roof of a senior housing complex collapsed during the storm. The severity of those injuries was unknown.

"We know there is widespread devastation," Rockport Mayor CJ Wax said during a Saturday morning interview with The Weather Channel. "I think it’s safe to say we took a Cat. 4 (hurricane) right on the nose, and we’d appreciate everyone’s prayers."

Officials estimate that 40 percent of residents did not heed voluntary evacuation orders and remained in the city as Harvey roared ashore. 

(MORE: Here's Why Harvey Grew Into a Monster)

About 128 people were evacuated from a Fairfield Inn in Rockport after the hotel suffered severe damage, according to a National Weather Service report.

Officials in several coastal Texas towns asked residents to stay away until they could get a better scope of the destruction caused by Hurricane Harvey, now a tropical storm, during its Friday night landfall.

A curfew was in place in Port Lavaca because all power, water and sewer services were down, the city's police department said in a Facebook post.

In Port Aransas, an island community with a population of 3,800, Mayor Charles Bujan told The Weather Channel there was widespread damage – including a trailer park that is 100-percent destroyed. Officials say they were unable to fully survey Port Aransas Saturday because of "massive" damage. Police and heavy equipment were only able to make it into the northernmost street, the AP also said.

"I can tell you I have a very bad feeling and that's about it," Bujan said.

The U.S. Coast Guard rescued four people from the vessel Signet Enterprise Saturday near Port Aransas, according to DVIDS. In total, at least 20 people have been rescued from vessels.

Possible Tornadoes Leave Behind Damage in Nearby Cities

Storms that hit parts of Texas during Saturday left behind damages that may take days to be inspected by survey crews to determine if they were indeed tornadoes. Damage from these storms may be very similar to damage seen close to where the eyewall of Harvey pushed through along the coast at peak intensity, according to weather.com meteorologist Jonathan Belles.

Photos and videos posted to social media showed a possible tornado rolling through a neighborhood in Cypress, Texas, Saturday.

According to reports on the ground, it "touched town near the Berry Center in Cypress and damaged at least one home and a fence next door to the home." No injuries were reported.

More than 50 homes in Missouri City were damaged by a storm when it hit the Sienna Plantation neighborhood, KHOU.com reports. Several homes had the roofs torn off and collapsed walls. A responding deputy was reportedly blown off the road.

"We were here last night, and we basically had the place sealed up so water couldn't get in," the manager, only identified as BJ, told ABC13. "My partner called me in the morning at 6 o'clock and said everything was destroyed. A tornado had came through around 5:30 and crossed I-10. Totally ruined the office."