CHICAGO (AP) — The National Weather Service said a tornado touched down near Chicago’s O’Hare International Airport on Wednesday following warnings of severe weather for the city.

A confirmed tornado was on the ground around 7 p.m., according to the National Weather Service in Chicago.

“This tornado has been touching the ground intermittently so far and is moving east. There are additional circulations along the line south of O’Hare. Seek shelter if in the warned area,” it said.

Video from TV stations showed hundreds of people taking shelter in an O’Hare concourse. Some 166 flights were canceled and nearly 500 were delayed, according to the flight tracking service FlightAware.

The National Weather Service issued two tornado warnings for portions of the city Wednesday evening. Tornado sirens sounded at least twice across Chicago, warning people to take cover and ringing through the city’s buildings.

Lynn Becker, a longtime Chicago resident, posted video to Twitter with the sirens sounding out across the city’s iconic skyline.

“I’m in a 60 story apartment building so my options are somewhat limited,” he said. “We have to, I assume, go into the core of the building.”

Becker said news of the storm was featured across local media.

“There’s a certain panic when you’re watching a TV screen and everything is in red … but the hope is that the damage is minimal,” he said.

The weather service quoted an unidentified emergency manager as saying a roof was blown off in the community of Huntley in McHenry County and a trained weather spotter saying trees were uprooted and roofs blown off in Cook County, where Chicago is located.

Earlier Wednesday, the weather service’s Storm Prediction Center had said there was an enhanced risk for severe weather, including tornadoes in northern Illinois, including Chicago.

Many tornadoes have struck in the Chicago metropolitan area, and several have hit within the city limits of Chicago, according to the weather service. Between 1855 and 2008, the weather service recorded 92 significant tornadoes in the Chicago metro area. The deadliest formed in Palos Hills in Cook County on April 21, 1967. The twister traveled 16 miles (26 kilometers) through Oak Lawn and the south side of Chicago, killing 33 people, injuring 500 and causing more than $50 million in damage, according to the weather service.