At least seven people have been killed and two more reported missing after an unusual storm system hit the Midwest and Southeast United States, spawning more than a dozen tornadoes of varying intensities. With nearly one in three Americans expected to be traveling this week for Christmas, both road and air passengers have been affected as well, NBC reported.

Four people, including a 7-year-old boy, were killed in Mississippi late Tuesday and two people were reported missing as tornadoes moved through the northern parts of the state. The Mississippi Emergency Management Agency said at least 40 people were injured. Authorities in parts of the state are conducting a house-by-house search-and-rescue operation, since high-speed winds have damaged many homes, BBC reported.

A man and a woman were reported killed in the storm by the Tennessee state health department, which did not provide any more details. Gary Rogers, the state's emergency management director, told Fox news affiliate WZTV that two other people were missing.

In Arkansas, an 18-year-old woman was reported killed and an 18-month-old child was taken to hospital after a tree was uprooted and tossed on a house.

Officials have reportedly warned residents in affected areas of Mississippi, Tennessee, Arkansas, Illinois, Missouri and Kentucky that outdoor Christmas decorations could turn into dangerous projectiles due to the high-speed winds, and advised people not to put up such decorations.

While unusual, this isn’t the first time that storms have hit the U.S. at this time of the year. A tornado had hit Mississippi a year ago, killing five people and injuring dozens. In 2012, a storm on Christmas day spawned several tornadoes, which had damaged homes from Texas to Alabama.