Tornados sweeping through the US Midwest states of Illinois, Indiana and Kentucky have killed at least five people.
Several hundred others may have been injured in the fast-moving storms.
Forecasters say up to 53 million people could be affected. Hailstones the size of tennis balls have been reported, according to the BBC.
The rapid-moving storm – with winds of up to 68mph – is continuing its way east.
All the deaths were reported in Illinois, which was the hardest hit state.
The US National Weather Service warned of a “particularly dangerous situation” for parts of the central US.
“Several rapidly moving, intense tornadoes, severe thunderstorms, large hail events and damaging winds are expected in these watch areas,” it said.
American football fans were evacuated from a stadium in the centre of Chicago as one tornado moved through the city suburbs.