Authorities in Trenton say they are investigating the cause of a Sunday morning house fire that left three firefighters injured.

The flames broke out at 4:30 a.m. at a vacant home on Cook Avenue and spread to two connected houses that were occupied.

Nearby residents were able to evacuate safely, according to police.

Authorities say one of the firefighters injured was treated for minor burns and released. Two others were treated for first and second degree burns and in stable condition. All three firefighters are expected to be OK.

Authorities say the cause of the fire could not be determined at this time.