Rescue efforts resumed Wednesday outside this Texas-Mexico border city where a tornado killed at least seven people, destroyed two schools and damaged more than 20 homes. Three other people died a few miles away in Piedras Negras, Mexico.

Five victims were in one mobile home. "It was a whole family, and they were all together, probably like they were huddling," said police Officer Ezekiel Navjas.

Lightning was blamed for an 11th death Wednesday as the huge weather system plowed through the U.S. Midwest and South. The bolt started a fire in Louisiana that killed a 101-year-old man, authorities said.

• Check out FOXNews.com's Natural Disasters Center.

The huge weather system has spun off tornadoes in Oklahoma and Colorado, caused flooding in Iowa and Nebraska and piled snow in the Rockies.

In Dallas, where winds peeled the roofs off some buildings, American Airlines canceled about 200 flights and diverted about 80 others, spokesman Billy Sanez said.

The Dallas-Fort Worth International Airport's flight control tower was temporarily evacuated Tuesday night but the airport remained open, said Ken Capps, the airport's vice president of public affairs.

Elsewhere, as much as 3.5 inches of rain fell Tuesday on western and central Iowa, causing at least one landslide that buried part of Interstate 29 in trees and mud. No vehicles were driving through the spot at the time, officials said.

In Colorado, six buses carrying at least 60 children were stranded when the storm dropped more than 12 inches of snow in about two hours, said Rob Finley, assistant fire marshal for El Paso County.

Tornados touched down in Colorado and Oklahoma, but no injuries were reported.