President Barack Obama declared Louisiana was in a state of disaster on Sunday after a historic flood left at least five people dead, with emergency crews working to rescue thousands more.

Governor John Bel Edwards said more than 10,000 people are now in shelters and more than 20,000 people have been rescued across south Louisiana.

More than a foot of rain fell overnight on Friday - in a deluge estimated to occur once every 500 years, according to the Pacific Standard.

In shocking photos showing the devastation, caskets that had washed up from a graveyard floated down the street in Denham Springs, Louisiana.

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In shocking photos showing historic floods in Louisiana, caskets that had washed up from a graveyard floated down the street in Denham Springs

President Barack Obama issued a declaration of disaster on Sunday for Louisiana, where at least five people have died

Governor John Bel Edwards said more than 10,000 people are now in shelters and more than 20,000 people have been rescued across south Louisiana

The 'unprecedented' flooding devastated Louisiana, where three months' worth of rain fell overnight on Friday

Four people were reported dead, with another body recovered later on Sunday from a flooded vehicle in East Baton Rouge Parish

Four people have been reported dead, said Devin George, the state registrar for vital records, earlier Sunday.

A woman's body was later recovered by divers from inside a flooded vehicle in East Baton Rouge Parish, appearing to raise the death toll to five.

Witnesses said the woman was seen Saturday night attempting to turn around in high water when her vehicle was swept away, said Casey Rayborn Hicks, a spokeswoman for the sheriff's office.

In one dramatic rescue Saturday, two men on a boat pulled a woman from a car that was almost completely underwater, according to video by WAFB.

The woman, who's not initially visible on camera, yells from inside the car: 'Oh my god, I'm drowning.'

One of the rescuers, David Phung, jumped into the brown water and pulled the woman to safety.

After the woman pleaded with him to save her dog, Phung went underwater and resurfaced with the animal.

But things could get worse since the National Weather Service forecasts heavy rain from the Gulf Coast as far north as the Ohio Valley through Monday, with a threat of flash flooding.

The National Weather Service forecasts heavy rain through Monday, with a threat of flash flooding (pictured, residents before they were evacuated by Louisiana Army National Guard)

Edwards warned: 'Even with the sunshine out today intermittently, the waters are going to continue to rise in many areas, so this is no time to let the guard down' (pictured, a stranded car on Interstate 12 in Livingston Parish)

Obama's declaration of disaster allows federal aid to reach the parishes of East Baton Rouge, Livingston, St. Helena and Tangipahoa, hit hardest by the floods

Emergency officials said they were still working on strategies to rescue an undetermined number of people trapped by the waters

In Livingston Parish, phone service was spotty due to the high waters and most shelters were full

The Ochsner Medical Center in Baton Rouge has evacuated about 40 patients and is expected to evacuate another 10-15 (pictured, cars backed up on a flooded road)

While the brunt of the storm that brought torrential rains was moving west toward Texas, Louisiana residents should remain cautious, the governor said at a news conference.

'Even with the sunshine out today intermittently, the waters are going to continue to rise in many areas, so this is no time to let the guard down,' Edwards said, calling the flooding unprecedented.

Obama issued the disaster declaration after speaking with Edwards, making federal aid available in the parishes of East Baton Rouge, Livingston, St. Helena and Tangipahoa, hit hardest by the floods.

Edwards said in a statement that other parishes could be added to the list.

Emergency officials still were working on strategies to rescue an undetermined number of people trapped by the waters.

'We're very much still in the search and rescue mode,' said James Waskcom, director of the state's Office of Homeland Security and Emergency Preparedness.

In Livingston Parish, phone service was spotty due to the high waters and most shelters were full.

A Greyhound Bus traveling from Memphis, Tennessee, to Baton Rouge was diverted to a shelter because of flooded roadways.

Robert and Gwen Arceneaux left their house on Sunday and reached a shelter through a National Guard truck. But Robert is in need of medication for his lung cancer

Louisiana State Police Colonel Michael Edmonson said helicopters were transporting food and water to those still trapped by floods

Helicopters also were transporting some seriously ill people to areas outside the high waters

Some 1,700 members of the Louisiana National Guard have been deployed for rescue efforts

Authorities worked tirelessly to save people from cars stranded on a miles-long stretch of Interstate 12 (pictured). The governor later said on Twitter that everyone had been rescued

Robert and Gwen Arceneaux gathered up their dogs and a few bags of belongings and fled out the back door of their house after enduring a sleepless night as they watched the floodwater creep into their home.

They eventually waded through waist-deep water to a passing National Guard truck, joining the more than 20,000 people rescued from their homes in a still-growing tragedy across southern Louisiana.

Now safe at a movie studio-lot-turned-shelter their worries weren't over, as they tried to get medication for Robert, who suffers from lung cancer.

Across southern Louisiana Sunday, residents scrambled to get to safety as rivers and creeks burst their banks, swollen from days of heavy rain that in some areas came close to two feet over a 48-hour period.

About 5,000 people had been forced to sleep in shelters overnight around the state, said Marketa Walters, head of Louisiana Department of Children and Family Services.

Louisiana State Police Colonel Michael Edmonson said helicopters were transporting food and water to those still trapped by floods. Helicopters also were transporting some seriously ill people to areas outside the high waters.