Alan Freeman and Brandon Schmidt (L to R) assess the damage to Brandon's brother's home after a powerful tornado struck Clarksdale, Mississippi, December 24, 2015. [Photo/Agencies]

DALLAS - Storms hit the US South, Southwest and Midwest over the Christmas holiday weekend, unleashing floods and tornadoes that killed at least 43 people, flattened buildings and snarled transportation for millions during a busy travel time.

The bad weather or threat of it prompted the governors of Missouri and New Mexico to declare a state of emergency for their states.

Flash floods killed at least 13 people in Missouri and Illinois.

In Missouri, emergency workers have evacuated residents from their homes and conducted dozens of water rescues, Governor Jay Nixon said on Sunday. He said at least eight people had been killed and numerous roadways had been closed.

Nixon declared a state of emergency, saying continued rains would make already widespread flooding conditions worse.

Three adults and two children were in a car near the village of Patoka, Illinois, 85 miles (137 km) east of St. Louis, Missouri, when their vehicle was washed away by floodwaters on Saturday night, according to Marion County Coroner Troy Cannon.

In Texas, at least 11 people were killed in the Dallas area over the weekend by tornadoes, including one packing winds of up to 200 miles per hour (322 km per hour). The twister hit the city of Garland, killing eight people and blowing vehicles off highways.