Search-and-rescue boats, high-water vehicles and even jet skis patrolled flood-swollen streets while a levee south of Houston breached Tuesday under the strain of Tropical Storm Harvey's easterly trudge toward Louisiana.

River levels marched higher, swelled by days of relentless rain. Authorities in Brazoria County announced a levee breach at Columbia Lakes.

"GET OUT NOW!!" the county tweeted.

The Brazos River at Richmond, about 30 miles south of Houston, was expected to crest at 59 feet by Thursday — four feet greater than the record high set last year.

“The threat is now moving from rain to river,” KPRC-TV meteorologist Britta Merwin said.

President Trump and first lady Melania Trump participate in a briefing on Harvey relief efforts Tuesday, Aug. 29th in Corpus Christi, Texas. 

President Trump arrived in Texas on Tuesday, meeting Gov. Greg Abbott in Corpus Christi and holding a news conference but staying out of Houston so as not to add to the chaos there.

The storm remained adrift over the Gulf of Mexico on Tuesday, already having dumped more than 40 inches of rain in parts of Houston. A National Weather Service gauge southeast of Houston recorded 49.32 inches from Harvey — the highest rainfall total from a tropical storm or hurricane in the contiguous 48 states.

The storm is expected to dump an additional 7 to 13 inches of rain through Friday over the upper Texas coast and into southwestern Louisiana.

Still, Mayor Sylvester Turner tried to be optimistic in a news conference Tuesday.

"My hope is that once we get past the next 24 hours that the situation in the city of Houston will significantly improve," Turner said.

Emergency responders have conducted more than 3,500 boat and air rescues, and the number continued to climb, Police Chief Art Acevedo said. The shelter set up at the George R. Brown Convention Center in downtown Houston was packed with more than 9,000 evacuees — nearly double its planned capacity.

Still, no one was being turned away from shelters in the region.

"Last night in Texas, 17,000+ people sought refuge in shelters," the American Red Cross tweeted Tuesday. "We're providing safety & comfort to rescued families."

Turner said two or three more shelters would open soon. He said the city would continue to operate with essential personnel at least until Thursday, but he urged city employees to help out at shelters and with other emergency duties. And he again addressed criticism that Houston did not call for an evacuation in advance of the storm.

“You cannot evacuate 6.5 million people within two days,” he said. “You cannot. That would be chaotic... you would be putting people more in harm’s way.”

Volunteer search and rescuers from Passion Pursuit film production company launched their motor boat near Bray Bayou and Loop 610 to rescue flood victims in the Meyerland neighborhood after Hurricane Harvey.

Outside help continued streaming into Houston. Search-and-rescue crews from Florida, California, Utah and other areas staged at different trouble spots around town. Walmart was shipping 2,000 kayaks to the area to help stranded residents.

No official death toll had been released, and authorities said it could be days before the full extent of the storm is known.

“We know in these kind of events that, sadly, the death toll goes up,” Acevedo told the Associated Press. “I’m really worried about how many bodies we’re going to find" when the water recedes.

Acevedo also said police had arrested a group of four armed "hijackers" and three looters. He issued a warning to would-be offenders.

"Word to the wise — don't come to Houston because you are going to be caught," he said. He promised swift arrest and a push for tough prosecutions and sentences for criminals who "take advantage of people and prey on them in these circumstances. That is despicable behavior."

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Gov. Greg Abbott said the focus remained on saving lives, but that the recovery effort across the region would begin soon.

"We will rebuild and make it better than ever," Abbot said.

Evacuees described turmoil, uncertainty — and relief to have survived.

Surrounded by people taking a smoking break outside the convention center Monday night, Danielle Brown hugged her boyfriend, Lorenzo Harps. They arrived Sunday night after being rescued by boat from a ground-level Houston-area apartment.

They awoke about 11 p.m. Saturday amid water a few inches deep.

“Everything was already flooded,” Brown said late Monday, huddled beneath a relatively dry overhang as rain poured down. “It was about to our feet, and it just kept rising. We had to move to the top floor, to a neighbor.”

Before moving up, they tried putting electronics, clothes and keepsakes on counters and shelves. The water climbed to 3 feet within hours, and rescuers evacuated them by boat the next day.

“They were strictly business,” Harps said of the rescuers’ efforts.

Now, the couple is stranded at the shelter. They shared a phone, which fell in the water during the chaos — something they can only laugh about now. Brown’s recently purchased Saturn sedan was destroyed.

The wrath of Harvey is Brown’s first brush with a tropical storm or hurricane. And she had one message to the untold numbers of residents experiencing a similar crisis as rescue efforts intensify.

“Be prepared. Be cautious,” she said. “Grab only what you need. Grab your life.”

Contributing: Doyle Rice, USA TODAY; Daily Advertiser in Lafayette, La.