Severe storms unleashing tornadoes, heavy rain and hail across the southern and central United States left at least six people dead and dozens injured while snarling traffic as holiday travel began in earnest for the Christmas holiday weekend.

Vehicles are seen driving in traffic on the Long Island Expressway in the Queens borough of New York December 23, 2015.

The stormy weather scrambled winter getaway plans in Florida even as dreams of a white Christmas melted in northeastern swaths of the country where unseasonably warm temperatures prevailed.

A large tornado raked a 100-mile stretch of northern Mississippi in the late afternoon, demolishing or heavily damaging dozens of homes and other buildings in a six-county area before plowing into Tennessee, authorities said.

Three people were confirmed dead from the storms in Mississippi, including a 7-year-old boy, two more in Tennessee and one in Arkansas, according to emergency management and law enforcement officials in the region.

Among the storm-related fatalities in Mississippi were a man and a woman, both in their 60s, who were killed separately when a tornado destroyed their homes in Benton County, Mississippi, said state Highway Patrol Sergeant Ray Hall.

A few more people remained unaccounted for as search teams combed through debris after dark, he said.

Gregg Flynn, a spokesman for the Mississippi Emergency Management Agency, reported more than 40 injuries in the six hardest-hit counties.

In Tennessee, clobbered by multiple twisters, state Emergency Management Agency spokesman Dean Flener confirmed two storm-related fatalities in Perry County - one male and one female of undetermined age.

"It got to middle Tennessee and went 'Ka-pow'," Flener said of the storm system.

An 18-year-old Arkansas woman died and a toddler was injured when a tree crashed into her house after being uprooted by powerful winds during a storm, according to emergency officials there.

States from Louisiana to Illinois were under a tornado watch on Wednesday. Possible tornado damage was also reported near Indianapolis, Indiana.

More than 100 million Americans were expected to travel during the holiday period beginning Wednesday - 91 million of them by car, according to the American Automobile Association.

In the Northeast, where warmer weather spared drivers the crippling delays wrought by winter storms, traffic was heavy, with more rain expected until Thursday in and around New York.

In New Jersey alone, more than 2 million vehicles had been expected to hit the roads on Wednesday.

In California, 11 million people were planning to travel by car between Dec. 23 and Jan. 3, and another one million were planning to fly to their destinations.

Meanwhile, the National Weather Service said it received reports of hail as large as golf balls falling in parts of Alabama, Arkansas, Illinois, Kentucky, Missouri and Oklahoma.

Weather Service meteorologist Greg Carbin said travelers in Georgia, New York, Tennessee and Ohio were likely to experience some weather-related delays on Wednesday evening.

Travel in Minnesota was also briefly disrupted when Black Lives Matter activists protesting against a spate of police killings of unarmed black people nationwide, shut down roadways to both terminals at Minneapolis-St. Paul International Airport, an airport spokesman said.

Protesters in California blocked traffic near San Francisco International Airport on Wednesday as part of the same "Black Xmas" protest.

Source: Reuters