(CNN) -- Heavy rains slammed parts of the Southeast for a second straight day Thursday, part of a series of storms that has killed four people, flooded homes and wrecked highways.
Flash flood watches were in effect Thursday from eastern Texas through Louisiana and up into the Mississippi River Valley -- including Arkansas, Tennessee, Missouri and southern Illinois.
Some bayous and creeks near Shreveport are expected to crest at levels not seen since 1991, according to CNN meteorologist Michael Guy.
State offices in 17 Louisiana parishes were closed Thursday, according to CNN affiliates KTAL and KMSS. The northwest part of the state could see another 8 to 10 inches on top of the drenching it received Wednesday, when some isolated locations got more than 14 inches.
Residents also may be in for a soggy weekend. The current system, which has caused this wet weather pattern, is expected to remain over the lower Mississippi River Valley through the weekend, according to Guy.
That means the region is at risk of further flooding until Monday.
At least four people have been killed in storms across the region, officials said. In Texas, a man died after his kayak capsized in Dickinson Bayou, near Galveston, police said.
Three people have been killed in Louisiana, Gov. John Bel Edwards said Thursday. In one case, a driver died when his vehicle was swept off the road in floodwaters in Bienville Parish, a spokesman for the state's Office of Homeland Security and Emergency Preparedness said.
Edwards declared a state of emergency in 22 Louisiana parishes, and the National Weather Service issued a flash flood emergency for several parishes.
Officials warned that floodwaters could rise above a levee and place thousands of homes in jeopardy.
After more than 14 inches of rain fell in Bossier Parish, officials there said they had closed at least 100 roads and had issued a mandatory evacuation order for residents of 3,500 homes that could be at risk if floodwaters keep rising.
The levee protecting parts of Bossier was "stressed" and overtopped in some areas, but so far it has not failed, CNN affiliate KTBS reported. Bossier Parish Sheriff Julian Whittington said Wednesday that floodwaters could rise above the Guideline Levee.
"We'll be out there in full force the rest of the evening and night, as long as it takes," Whittington said. "We encourage everyone to get prepared, and try and evacuate. ... You do need to move out."
The flooding, Whittington said, is a "dangerous situation."
"We've had folks who had to be rescued off rooftops, people rescued from cars, clinging to trees," sheriff's spokesman Bill Davis said.
The sheriff's office posted video showing rushing water, pickups stranded in floodwater and people piling sandbags to protect their homes.
Cathy Little of Shreveport said she's seen flooding there before, but never like this.
She posted videos of flooding in the area on Instagram. One showed a neighbor's home surrounded by water.
Parts of Arkansas and Texas have also endured heavy rainfall.
More than 10 inches of rain has fallen in Searcy, Arkansas, since Monday. Longview, Texas, has seen more than 8 inches, according to the National Weather Service.
Forecasters warned people to stay off the roads in areas facing heavy rains.
"Most flood deaths occur in vehicles," the National Weather Service said.
Flooding is the leading weather-related cause of death over the last 30 years, according to CNN meteorologists Jennifer Gray and Monica Garrett.
The severe storm risk will remain throughout Thursday, with cities such as New Orleans and Jackson, Mississippi, possibly feeling the impact.