INTERNATIONAL FALLS (AP) - Canadian National Railway officials are working around the clock to rebuild an old wooden railroad bridge that burned and collapsed near Minnesota's northern border.

Koochiching County Sheriff Perryn Hedlund says officials started removing debris from the bridge and three train cars hours after the bridge caught fire and then collapsed Wednesday.

The collapse blocked a Canadian National line that runs from Prince Rupert, British Columbia, to Chicago. It crosses the Rainy River, which forms part of the U.S- Canada border, at Ranier, Minnesota, just east of International Falls. It's one of the busiest rail crossings on the border. All rail traffic through Ranier has been halted.

Hedlunch says officials are "working around the clock" to rebuild the bridge.

The sheriff's office and state fire marshal are investigating the fire's cause.