An early-morning train derailment in the St. Clair River Tunnel linking Sarnia, Ont., and Port Huron, Mich., slowed international train traffic, but resulted in no injuries.

About 40 rail cars were involved in the incident in the one-lane tunnel.

CN confirms train derailed at 4:30am when approx 40 cars left the track. 52000 litres of sulphuric acid was leaked and is now being contained. St. Clair River and public not in danger. <a href="https://t.co/Z1DZgbrBI3">pic.twitter.com/Z1DZgbrBI3</a> —@AmyDodgeCBC

In a statement, CN Rail spokesperson Jonathan Abecassis confirmed that approximately 52,000 litres of sulphuric acid leaked from one car.

Abecassis added that the sulphuric acid is "contained to the site of the derailment and poses no danger to public safety or to the St. Clair River."

Port Huron city manager James Freed, who posted on Facebook that he was at the scene, said there were no injuries or threat to public safety.

According to Freed, Homeland Security and Emergency Management had been briefed on the situation.

Larry Lloyd, with CN Rail, confirmed it was responding to an incident in the tunnel.

An early-morning derailment inside the St. Clair River tunnel between Sarnia, Ont., and Port Huron, Mich., slowed international train traffic, but resulted in no injuries. (James Freed/Facebook)

According to Lloyd, "derailed" does not necessarily mean the entire train car flipped over.

"It could mean just a wheel is off or something like that."

Sarnia Mayor Mike Bradley said most of the derailment is on the Port Huron side of the tunnel.

CN Rail initially said 30 cars were affected, though it later confirmed that "approximately 40 cars have derailed in various positions within the tunnel."

Bradley had been told there were 46 cars. According to Bradley, 45 of them were carrying automotive parts.

"I don't know at this point, but I think the real issue is going to be that this is the major tunnel between Canada and the U.S. for rail," said Bradley. "What is the disruption going to be?"

Bradley didn't have numbers on how many trains pass through the tunnel daily, but estimated it at 50 or 60 a week.

There is no word on the extent of damage to the track or tunnel — the first full-size underwater tunnel built in North America.

(CBC)

Transportation Safety Board of Canada is deploying a team of investigators to gather information and assess the situation.

The St. Clair Tunnel first opened in 1891 and was used until 1995 when it was replaced by a new larger tunnel. Originally, only freight trains used the tunnel, with passenger rail beginning to use it in 1892. When the replacement tunnel opened, it was large enough to accommodate all freight cars in service at the time in North America, allowing rail ferries to retire.

The tunnel spans about 1,800 metres, but less than 200 metres is under water. It was officially renamed the Paul M. Tellier Tunnel in 2004, but is regularly referred to by its original name, the St. Clair Tunnel.