The twister traveled down one of Hattiesburg's main streets and caused what officials described as major damage, officials said, hitting several buildings on the campus of the University of Southern Mississippi. Kyle Hopkins, emergency operations director for surrounding Forrest County, said officials hadn't confirmed injuries. There were reports of several people hurt elsewhere in the state.
"We had a tornado touch down. We have a lot of damage," Hopkins said.
The university released a statement saying that several buildings had been damaged but that no injuries were reported. Campus police have declared a state of emergency and asked anyone not on campus to stay away.
The storm overturned and damaged vehicles and threw debris around parts of the campus.
Pictures posted on Facebook by WDAM in Hattiesburg showed rows of trees flattened in the Oak Grove area and damage to commercial buildings.
To the west, Marion County emergency director Aaron Greer says three injuries have been reported in the community of Pickwick, about seven miles south of Columbia. He says two people were taken to hospitals, but the third didn't have the injury examined.
Greer says one mobile home was destroyed, three other structures have major damage and several have minor damage.
National Weather Service meteorologist Joanne Culin says there have also been reports of injuries in Marion County.
Nasty weather has settled in on much of Louisiana and Mississippi, including tornado or flash flood watches.
The National Weather Service says bad weather is likely to stretch into Fat Tuesday in southeast Louisiana. Jefferson Parish has canceled a Monday night parade.
Associated Press writer Janet McConnaughey in New Orleans contributed to this report.