The death toll from historic flooding in Louisiana rose to 13 Thursday as receding waters exposed the extent of devastation in the hard-hit southern US state.

The highest number of confirmed fatalities was in East Baton Rouge parish where five people were dead, Shauna Sanford, a spokeswoman for Louisiana Governor John Bel Edwards, said.

The parish's sheriff's office said it had "shifted phases from search and rescue to public assistance and crime prevention."

Officials in other areas also said rescue operations were slowing.

"Assessments are beginning in areas where the water has receded," Livingston Parish Sheriff Jason Ard said Thursday in a statement.

Secretary of Homeland Security Jeh Johnson was in Baton Rouge Thursday, reviewing the emergency response and recovery efforts. He is expected to join other officials for a news conference at 1:45 pm Central time (1845 GMT).

Complicating the recovery were possible showers and thunderstorms in parts of Ascension parish -- which is further south from Baton Rouge and also one of the hardest hit.

Parish officials said flood waters there were receding at a rate of one inch (2.5 centimeters) per hour in some places, while holding steady or still slightly rising in others.

Where the land had dried out, residents picked through what was left of their sodden homes and belongings, trying to salvage what they could before mold sets in.

The Louisiana National Guard said it has so far distributed 32,000 ready-to-eat meals and 2,200 cots to survivors.

Electricity was slowly being restored. The number of customers without power was less than 16,000, down from a peak of 40,000.

While many areas were drying out, the National Weather Service forecast that all waterways would not fall below flood stage until as late as Friday.

Twenty-two of the state's 64 parishes, Louisiana's equivalent to counties, have been declared disaster areas, designations that free up federal disaster assistance.