Investigators said Thursday there is "no sign of foul play" in the fire that destroyed a rail bridge on a key Canadian National route through northern Minnesota.

"This investigation produced evidence of a mechanical failure," said a statement from the Koochiching County Sheriff's Office.

The crew of a southbound Canadian National train reported a fire as they approached the heavily trafficked bridge early Wednesday just north of Ericsburg. The train couldn't stop in time, and the bridge burned and collapsed, tipping two rail cars full of potash, a fertilizer, onto the banks of the Rat Root River.

The bridge collapse blocks a rail artery that runs from British Columbia to Chicago.

No one was injured, and railroad analysts say Canadian National will be able to rebuild the bridge within days.