The fire at 10 Spruce St., was contained to the living room. (Google Maps)

Saint John investigators are trying to determine the cause of a fire early Sunday morning that left 15 people displaced.

Fire crews were called to 10 Spruce St., north of the Throughway, at about 12:30 a.m.

When they arrived at the scene, they found heavy smoke on the first floor and fire in the living room area, officials said.

Firefighters contained the fire to one room, but residents will not be allowed back in until the building is ventilated and cleaned up.

The Red Cross has helped the residents find temporary accommodations.