Three firefighters were injured - one seriously - and two civilians were hurt in a massive Washington Heights blaze yesterday morning that took 168 firefighters two hours to extinguish.

The four-alarm blaze, which is believed to have begun on the first floor of 1274 St. Nicholas Ave., was called in at 10:34 a.m. Thirty-nine units responded, extinguishing the fire by 12:38 p.m.

The seriously injured firefighter was transported to St. Luke's Roosevelt Medical Center, where he was expected to recover, said an FDNY spokesman. The other two fire fighters and civilians were treated at the scene.

According to Property Shark, the six-story 1910 building has seven commercial units and 43 residences. The Red Cross was on the scene yesterday to help residents who were displaced.

The cause of the fire is under investigation.