Norwich — Firefighters worked into the night Tuesday trying to completely extinguish a stubborn smoldering pile of burning railroad ties.

The fire encompassed more than half of a 10-by-60-foot stack of creosote-treated timbers on Providence and Worcester Railroad property between Laurel Hill Avenue and the Thames River.

The cause of the fire is apparently suspicious because there is no power source or known activity in the area where it started. Fire Marshal Jake Manke said it was too early to call it arson, but he said he has turned over investigation to the Norwich Police Department’s fire investigation team.

The fire was first reported at 6:10 p.m. as a camp fire and later as a possible brush fire, said Norwich Fire Battalion Chief Gregory Despathy.

A plume of acrid black smoke was visible from across the Thames River and in parts of the downtown area as city firefighters made their way to the source and discovered flames shooting from the pile of timbers.

The fire was about 50 feet away from several freight cars on the tracks and a short distance from Shetucket Iron & Metal, a scrap metal recycling facility on the same access road adjacent to Laurel Hill Avenue.

With help from the Laurel Hill Fire Department’s hose tender, firefighters uncoiled 2,700 feet of hose from a hydrant on Laurel Hill Avenue to reach fire engines along the railroad tracks. It took another 400 feet of hose to reach the fire.

The major part of the fire was knocked down within minutes, but flare-ups persisted after nightfall. Rail service was halted during operations and a representative from Providence and Worcester was expected to arrive at the scene later in the evening, Despathy said.

Despathy said firefighters were using firefighting foam to suffocate the parts of the fire buried deep in the timber pile. Temporary lighting was set up on the railroad tracks. An excavator was also called in from the city’s public works department.

“We’re going to have to tear that pile apart,” Despathy said.

He expected firefighters to remain at the scene for an “extended period of time,” Tuesday evening.

No injuries were reported.

g.smith@theday.com