National Weather Service meteorologist Brad Bryant said the worst weather was predicted south of U.S. Highway 82, which runs from Greenville to Columbus in Mississippi. He said there was "some risk" of severe weather, but heavy rain was the main concern.
Tornado watches, flash flood watches and severe thunderstorm watches stretched across parts of central and south Mississippi, but the biggest threat was heavy on saturated ground. That increases the chances of flash floods and uprooted trees.
There were no immediate reports of injuries.
Adams County Emergency Management Director Stan Owens said crews had to clean up some Natchez streets because of several mudslides early Thursday, but the city's main thoroughfares remained open. He said there were trees down around the county, including one that fell on a house in Natchez.
Natchez had 4-5 inches of rain from Wednesday evening to Thursday morning and more was falling, Owens said.
The National Weather Service said Clayton, La., northwest of Natchez, had 7.2 inches of rain over a 24-hour period and there were reports that some houses there had water standing in them.
Warren County, Miss., Emergency Management Director John Elfer said there was localized street flooding in parts of Vicksburg and two people were rescued from a car that stalled in flood water early Thursday.
Residents in Sharkey County reported flood water touching their homes, according to the weather service.
Downed trees were reported along the Natchez Trace and Mississippi Highway 547 near Port Gibson.