A three-alarm blaze erupted at Penn Station, disrupting subway service early Tuesday, officials said.

The fire broke out at an LIRR construction site underground around 2:20 a.m. at 33rd Street near Eighth Avenue and it took more than 150 firefighters about three hours to fight back the flames, authorities said.

Two firefighters suffered minor injuries and were taken to Bellevue Hospital, authorities said.

The A, C and E subway lines were bypassing the 34th Street station but service was restored at 6:30 a.m. with residual delays. LIRR service was not affected, officials said.

The fire was placed under control at 5:20 a.m., the FDNY said.

The cause of the fire has not yet been determined.

The MTA said commuters should give themselves extra travel time for the Tuesday morning commute.