By Emily Le CozJACKSON, Miss. (Reuters) - Severe thunderstorms menaced the U.S. Southeast on Wednesday, as emergency workers in Mississippi surveyed damage from tornadoes that killed at least four people and injured 20.As the storms moved eastward on Christmas Eve, damaging wind gusts and possibly more tornadoes threatened northern Florida, parts of Georgia and the Carolinas, according to the National Weather Service.The storm system was part of a front expected to bring hazardous travel conditions to much of the eastern United States, with rain expected to change to snow from Illinois to northern Michigan, the weather service said.Yet forecasters said the risk of severe weather appeared less than on Tuesday, when deadly tornadoes ripped through southeastern Mississippi."There is a lot of destruction here," said Brett Carr, a spokesman for the Mississippi Emergency Management Agency, speaking from the hard-hit Columbia, about 60 miles (100 km) south of Jackson.People were cleaning up debris and covering buildings with tarps on Wednesday, Carr said, with some buildings destroyed.The American Red Cross and the Salvation Army were in town distributing meals, he said.Mississippi Power reported that 3,600 customers lacked power as of late Tuesday, but crews were working to restore service. Pearl River Valley Electric Power Association reported 2,200 customers without power on Wednesday.Marion General Hospital in Columbia was running on a generator on Wednesday after treating more than 50 patients for storm-related injuries, according to hospital spokeswoman Millie Swan.While the hospital was not damaged in the storm, Swan said it was a "close call.""Just one street over it wiped out houses," Swan said.The twisters were unleashed by thunderstorms that tracked from Louisiana to central Alabama. Several homes were damaged in southeastern Louisiana, but no injuries were reported.As thunderstorms moved northeast, according to the weather service, severe weather could be seen by evening in parts of Virginia, eastern Kentucky, Ohio, West Virginia and western Pennsylvania.(Additional reporting and writing by Letitia Stein in Tampa, Fla.; Editing by Doina Chiacu)Join the conversation about this story Click here to read full news..