CHICAGO - DANGEROUS winds grounded hundreds of flights and interrupted shipping traffic on the Great Lakes on Tuesday as a massive storm system whipped the central United States and left tens of thousands without power.

Some 13 tornadoes were reported in five states as near hurricane-force winds ripped roofs off homes, damaged businesses and knocked down trees and power lines, the National Weather Service said.

The storm raced across Minnesota, Wisconsin, Illinois and Indiana in the morning, then ravaged Michigan, Ohio and Kentucky by midday and was forecast to then strike Canada and eastern states later on.

'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, Mr Slattery said.

Very strong winds '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.'

The powerful winds forced some schools to close and snarled the morning commute. More than 500 flights were cancelled at O'Hare and those still set to land or depart were experiencing delays of about 45 minutes, officials said.

Huge storm grounds US flights