Recovery crews and utility workers began cleaning up widespread damage on Thursday left by severe storms that spawned tornadoes across six states in the US South and Midwest, killing at least 14 people and destroying scores of homes.

Emergency declarations were issued in Mississippi and Tennessee, the two states hardest hit by severe weather on Wednesday that also complicated getaway plans for travellers looking to make the most of the long holiday weekend.

With about 100 million Americans expected to travel over the Christmas holiday, the National Weather Service forecast isolated severe thunderstorms from the mid-Atlantic region to the Gulf Coast and record warmth in New York.

The storm system packed high winds and triggered more than 20 tornadoes in Arkansas, Illinois, Indiana, Mississippi, Tennessee and Michigan on Wednesday, authorities said.

A large tornado tore a 100-mile (160-km) path through northern Mississippi, demolishing or heavily damaging more than 100 homes and other buildings before ploughing into western Tennessee, authorities said.

Mississippi Governor Phil Bryant declared a state of emergency in areas affected by the storm, saying 14 tornadoes had touched down in the state. Bryant said seven people were killed and one person was missing.

‘Everybody is pulling together here in Mississippi today to help respond to this disaster,’ Bryant said on CNN.

He said shelters had been set up and the full extent of the damage would not be known for several days. Mississippi authorities said some 40 people were injured and a 7-year-old boy was among those killed.

Three people died in Tennessee and an 18-year-old woman was killed in Arkansas when a tree crashed into her house, authorities said.

Thirteen counties in Tennessee suffered severe damage, with a post office destroyed and a state highway washed out.

Emergency crews in Mississippi, Alabama, and Tennessee were searching for several people reported missing. Scores were injured in the region.

A rare tornado touched down in Canton, Michigan, and about 15,000 homes in the state and neighbouring Wisconsin were without electricity. The weather service issued a gale force wind warning for Lake Michigan, where waves could reach 15 feet (4.6 meters).

About 500 flights were delayed or cancelled at Atlanta’s Hartsfield-Jackson airport as the area was hit by a thunderstorm.

Meanwhile, much of the northeast enjoyed balmy weather on Thursday, including New York, which surpassed its record for the warmest Christmas Eve reaching 71 degrees Fahrenheit (22 C).

Cold and snow were forecast on Christmas Day for the US.

Northwest, including temperatures in the teens in Montana and snow likely in Washington, Oregon, northern California, and Nevada.

Of the 100 million Americans travelling over the holiday, 91 million will use cars, according to the American Automobile Association.