Transportation Safety Board investigators are headed to the scene of a train derailment near Fort Frances.
The TSB says about 40 CN freight cars loaded with grain came off the tracks.
The short statement from the TSB didn't say whether anyone had been injured.
It's the second CN freight to derail in the past two days.
On Saturday six cars of a train carrying lumber left the tracks in Saskatchewan just west of Saskatoon.
And in Alberta there have been four train derailments in the past two months, including one in October that sparked a dangerous petroleum fire that forced the evacuation of the village of Gainford.