Officials say tornadoes have hit a large part of the US Midwest, killing at least five people in Oklahoma.
Twisters were also reported in Kansas, Iowa, and Nebraska as the storm front swept east.
The deaths occurred before dawn in the town of Woodward, Oklahoma, after warning sirens failed to sound.
Another twister caused widespread power outages and other damage in the city of Wichita, Kansas.
US tornadoes have already killed at least 39 people in 2012.