The bridge in Koochiching County belongs to Canadian National Railway. It carried more than 20 trains over the Rat Root River daily until it collapsed early Wednesday.
Canadian National spokesman Brent Kossey says the crew of a southbound train approaching the bridge reported a fire on the trestle just after 12:30 a.m. The train stopped after it had crossed the bridge. The bridge was destroyed, but the crew was not hurt.
Authorities are investigating the cause of the fire. The railroad is already working on a temporary replacement bridge.
In the meantime, all Canadian National trains through that area have been halted.