Twenty-one firefighters responded early Sunday morning to an apartment-building fire in downtown Tucson that caused $100,000 in damage, fire officials said.

The four tenants of the building, at 128 S. Herbert Ave. near East Broadway Boulevard, escaped without injury, said Capt. Trish Tracy of the Tucson Fire Department.

The cause of the fire has not been determined, but Tracy said the fire started in one apartment around 3 a.m.

One apartment was destroyed and the three others were damaged by smoke, fire officials said. The Red Cross is assisting the residents who were displaced by providing food and shelter, Tracy said.

Tracy said the firefighters did not hear a smoke detector when they responded to the fire.