PORT HURON, Mich. (AP) — Safety officials in the U.S. and Canada are looking into a multi-car train derailment in an international tunnel connecting Michigan's Port Huron to Sarnia, Ontario.

The National Transportation Safety Board says investigators have been sent to Port Huron, northeast of Detroit.

About 40 freight cars left the tracks around 4:30 a.m. Friday in the tunnel beneath the St. Clair River. Port Huron City Manager James Freed has said the wreck caused "significant damage" to the track and that it was not clear when the tunnel would reopen. No injuries were reported.

Canadian National Railway spokesman Jonathan Abecassis said about 13,700 gallons (51,859 liters) of sulfuric acid that spilled from one car had been contained.

The safety board says preliminary information indicates the derailment point is in the Canadian side of the tunnel.