A third rail fire in an East River tunnel has been extinguished after being discovered during Thursday’s rush hour, authorities said.

Firefighters from Manhattan and Queens were dispatched to the location after getting calls about Amtrak tunnel No. 2 just before 6:45 p.m., an FDNY spokesman said.

The problem was near the First Avenue hatch, and the MTA sent an engine from its Sunnyside Yard in Queens to investigate, an MTA source said.

The fire was put out about 7:50 p.m., the FDNY spokesman said.

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MTA spokesman Salvatore Arena called the fire “minor” and said three westbound trains were rerouted to a different tunnel.

A fire extinguisher was used to douse it, Arena said: “It was over in a few minutes.”