In Indiana, a twister touched down Monday evening in Pendleton, about 35 miles (56 kilometers) from Indianapolis. At least 75 homes were damaged there and in nearby Huntsville, said Madison County Emergency Management spokesman Todd Harmeson. No serious injuries were reported.

Pendleton residents were urged to stay in their homes Tuesday morning because of downed power lines and other dangers.

"People are getting antsy. I know they want to get outdoors, and I know they want to see what's going on in the neighborhood," Harmeson said. But he added: "We still have hazards out there."

Outbreaks of 50 or more tornadoes are not uncommon, having happened 63 times in US history, with three instances of more than 100 twisters, Marsh said. But Monday's swarm was unusual because it happened over a particularly wide geographic area and came amid an especially active stretch, he said.

As for why it's happening, Marsh said high pressure over the Southeast and an unusually cold trough over the Rockies are forcing warm, moist air into the central US, triggering repeated severe thunderstorms and tornadoes. And neither system is showing signs of moving, he said.

Scientists say climate change is responsible for more intense and more frequent extreme weather such as storms, droughts, floods and fires, but without extensive study they cannot directly link a single weather event to the changing climate.

AP