Dangerous winds grounded hundreds of flights at Chicago's O'Hare airport and interrupting shipping traffic on the Great Lakes Tuesday as a massive storm system whipped the central United States.

The National Weather Service warned that severe thunderstorms would send damaging winds and tornadoes crashing over Illinois, Indiana, Kentucky, Michigan, Ohio and Wisconsin.

"It's really blasting up there," said Pat Slattery, a weather service spokesman.

"It's going to blow and it's liable to last through tomorrow."

The intense low-pressure system was reaching levels equivalent to a category 2 or 3 hurricane and would likely set records in several states, Slattery said.

Very strong winds associated with the intense surface low "will allow the thunderstorms to organize into bands that will be capable of producing swaths of damaging winds and a few strong tornadoes," the weather service warned.

"State and local emergency managers are monitoring this potentially very dangerous situation."

Near hurricane force winds knocked down trees and power lines, damaged buildings and snarled the morning commute.

"I didn't even try to use my umbrella," said Chicago resident Mara Davis, 33, who was woken up several times in the night by the storm.

"The buses were running so slow, I opted for a cab. And it took forever because the roads were so bad."

Ships headed for safe harbor ahead of the storm which was predicted to kick up massive waves reaching as high as 27 feet (eight meters) on Lake Superior and 12 feet (3.7 meters) on Lake Michigan.

"We have three lakers that have come in and are docked for the day," said Adele Yorde, spokeswoman for the Duluth (Minnesota) Seaway Port Authority. "There are a couple thousand footers that we know of at anchor just outside the harbor. They'll be waiting out the storm there."

While the weather service was able to give boat captains ample warning of the oncoming storm, some were too far from port and will instead drop anchor in the lake and "position themselves so that they're not being broadsided by those waves," Yorde told AFP.

More than 300 flights were cancelled at O'Hare and those still set to land or depart were experiencing delays of about 30 minutes, officials said.

"A ground stop was in effect at O'Hare earlier today, meaning that there were no departures but there were arriving flights," spokeswoman Karen Pride said.

"The airport was never closed."