ALLENTOWN (AP) — A fire at an apartment complex has left at least four people injured.

Fire officials say residents were evacuated from the Gross Towers complex in Allentown after a fire broke out in a hallway around 10 a.m. Sunday, filling the building with heavy smoke.

Firefighters were able to contain the fire to a patch of carpet in the hallway and the fire was under control within 30 minutes. Residents who live in some areas of the building were soon allowed to return to their homes, but others were still waiting for clearance.

Authorities say it’s still not clear how the fire started.

One woman was taken to the hospital with undisclosed injuries, while three other people were being evaluated. Further details on their conditions were not immediately available.