Greg Hilburn and John Bacon

USA TODAY NETWORK

MONROE, La. — Rescue efforts intensified Sunday as historic rain that paralyzed much of southeastern Louisiana eased, while floodwaters continued to bring havoc to the battered region.

State Police helicopters delivered food and water to hundreds of motorists stuck for more than 24 hours in flooding near Baton Rouge.

Gov. John Bel Edwards said late Sunday that more than 10,000 people were in shelters and more than 20,000 people were rescued across south Louisiana. The Baton Rouge River Center, a major events location in the capital city's downtown, was to be opened Sunday as a shelter to handle the large numbers of evacuees.

Four people have been reported dead, said Devin George, the state registrar for vital records. The death toll rose Sunday when a man's body was found washed up on a riverbank in Tangipahoa Parish.

Parts of the area have been blasted by up to 25 inches of rain since Friday. The weather improved Sunday, but Edwards warned that flooding issues will continue for days.

"This is a serious event, ongoing," Edwards said at a Sunday news conference. "It's not over."

The Amite and Comite rivers were among those hit with record flooding. Jeff Gaschel, a hydrologist for the National Weather Service, said some areas of the Amite River won't crest until Monday. He said the area had similar rainfall amounts in 2001, but over a longer period of time.

The weather was improving, with forecasts calling only for occasional pop-up storms that are common in Louisiana this time of year, he said.

Rescue in Youngsville as hundreds flee flooded homes

"We are not in control as far as how fast these floodwaters will recede, and in fact they are still going up in some places," Edwards said. He urged residents not to venture out because the sun did. "We are asking everyone to be patient," he said.

Edwards, who was forced to flee the governor's mansion with his family due to flooding, said he sought a federal disaster declaration to expedite assistance to families and businesses.

"The simple fact is we are breaking records," Edwards said.

East Baton Rouge, Livingston, Tangipahoa and St. Helena parishes were officially declared federal disaster areas late Sunday, Edwards' office said.

No-name ‘monsoon depression’ not over yet

"I fully expect that more parishes will be added to the declaration on a rolling basis,” he said in a statement.

Ochsner Medical Center Baton Rouge said it was transferring about 40 patients, most critically ill, to other Ochsner facilities as a precautionary measure "to ensure ongoing continuity of care."

Some motorists were stranded for more than 24 hours. Boats were unable to provide rescues due to the sporadic areas of dry land, and state troopers were on the ground to aid those stranded, said Col. Michael Edmonson, the state police superintendent.

Why it's flooding, why the river's flowing upstream

Edmonson said troopers were rescuing those with medical conditions first, something Dugas confirmed. "We saw a couple of people who were ill taken away," she said.

"We have to address life and death situations first before quality of life," Edmonson said Sunday.

Dominique Dugas and her family of Lafayette, La., were rescued Sunday — her 29th birthday. She said they were heading to a funeral in Slidell on Saturday morning when they became stranded on I-12. Dugas said in a phone interview with USA TODAY NETWORK that her family walked to a convenience store and was shuttled by school bus to a shelter.

"We saw the helicopters landing just as we got on the bus," she said. "It wasn't as bad a birthday as you might think. I had my family, and we were able to help some people."

At 3 p.m. Sunday, I-12 Northbound was finally opened after 28 hours. Drivers said they helped each other out and shared food during the ordeal — one driver said he had "a power unit and a double bunk, so I took in six infants and their mothers so they could take care of their babies and stay cool."

About 1,700 National Guard troops were mobilized, with more on the way. State Transportation Secretary Shawn Wilson said more than 200 roads are closed. More than 5,000 people spent Saturday night in Red Cross shelters, some on floors because of a shortage of cots.

State government offices in 27 southern Louisiana parishes will be closed Monday, State Commissioner of Administration Jay Dardenne said.

The Coast Guard said it had rescued numerous people from from rooftops, automobiles and trailers.

Parts of Mississippi also felt the impact of heavy rains and flooding, and Gov. Phil Bryant declared a state of emergency for several counties. In Crosby, Miss., more than 50 people flooded out of a neighborhood will be housed Natchez shelter until at least Monday.

Contributing: WWL-TV, New Orleans, and The Associated Press; Bacon reported from McLean, Va.