BOSTON - A smoky fire in a downtown subway tunnel late Thursday forced the removal of passengers from trains and the shutdown of several lines.

Twenty people suffered minor smoke inhalation because of the fire, which started after 10 p.m. just north of the Downtown Crossing station in a Red Line tunnel near a congested area where several train lines intersect underground, authorities said.

While the fire was contained to that tunnel, smoke spread into several nearby stations and platforms, said Joe Pesaturo, spokesman for the Massachusetts Bay Transit Authority.

"The fire is out but the smoke was heavy, it was thick," he said.

As a precaution, the MBTA shut off power to the Orange and Green lines in the area. Silver Line buses near South Station were kept above ground.

Witnesses reported a heavy smell of an electrical fire.

Shannon Hebert of Malden told The Boston Globe the smoke came on fast as she was getting off the Red Line.

"The smoke was almost going as fast as me," she said. "I was hacking, coughing."

John Guy of Dorchester told the paper the smoke was so thick, he could not see. He said he had to hold on to someone he did not know to find his way out of the station. When he got out, he doubled over in pain, he told the newspaper.

Pesaturo could not say if the heavily traveled train lines would be reopened in time for the Friday morning commute.

"We have crews standing by that will jump into the tunnel," he said. "They will assess the damage and start making repairs as soon as possible."

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