A massive fire that forced the temporary closure of the Oak Street Bridge Wednesday afternoon is being called suspicious.

The second-alarm blaze broke out at a wooden railway trestle in South Vancouver shortly before 5 p.m., sending plumes of black smoke into the path of drivers on the bridge.

Officials closed the crossing for about half an hour while firefighters battled the flames, causing traffic to snarl along Oak Street. It was reopened once most of the smoke had cleared.

The cause of the blaze remains under investigation but Vancouver Fire and Rescue said it appears suspicious.

“We have a fire investigator on scene,” Deputy Chief Brian Godlonton said. “There was a report of people fleeing the scene prior to our arrival.”

The fire is also being investigated by police.

Almost 40 firefighters were dispatched to douse the flames, including members on a fire boat. They managed to knock it down quickly, but the trestle and two small outbuildings were badly damaged.

Despite the amount of smoke in the sky and the proximity to Vancouver International Airport, no flights were affected.

The trestle bridge, which links Vancouver and Richmond, is owned by the Canadian Pacific Railway. The company said the bridge is only used about once a week, and there were no trains in the area when the fire broke out.

Reports that the bridge was used to transport jet fuel are false, according to CP.