CHICAGO - A MASSIVE storm unleashed tornadoes for a second day on Wednesday, damaging property and causing flights to be cancelled as it whipped across the central and eastern United States and Canada.

Tornado watches were issued in seven states from Mississippi all the way up to New Jersey, as the unusually intense low-pressure system moved eastward.

North Dakota was under a blizzard warning as the tail end of the storm whipped up wind gusts of some 100kmh. Much of Ontario, meanwhile, was under a weather warning on Wednesday as the storm moved slowly eastward.

'This storm is so large it is affecting the weather in one way or another across the entire province,' Environment Canada said in a special weather advisory. 'The rain will switch to wet snow over western sections tonight, then during the day on Thursday in the east, giving a couple centimetres of the white stuff particularly in areas closer to the Manitoba border.'

Meanwhile, the Midwest continued to clean up after the storm grounded hundreds of flights, interrupted shipping traffic on the Great Lakes and left tens of thousands without power on Tuesday.

Some 24 tornadoes were reported on Tuesday in six states as near hurricane-force winds ripped roofs off homes, damaged businesses and knocked down trees and power lines, the National Weather Service said.

Huge storm grounds US flights