The National Weather Service advised people in the Chicago area to seek shelter on Wednesday night after a tornado was confirmed to be on the ground near O’Hare International Airport and moving east toward downtown.

“To repeat, a tornado is on the ground,” the Weather Service wrote in an advisory at 7:03 p.m. “TAKE COVER NOW! Move to a basement or an interior room on the lowest floor of a sturdy building.”

The Weather Service said that flying debris posed a threat to people outdoors and warned that mobile homes could be destroyed. There was some property damage, but no immediate reports of injuries or deaths, the authorities said.

A tornado warning was put into effect until 7:45 p.m. for Cook County, Ill., which includes Chicago, Cicero and Evanston, the National Weather Service said on Twitter.

A tornado watch is in effect for surrounding counties until 10 p.m.

Judson Jones contributed reporting.