A predawn fire Tuesday heavily damaged a Cobb County restaurant, authorities said.

The fire at Frontera Mex-Mex Grill on Powers Ferry Road near Windy Hill Road was reported just after 4 a.m. by someone hearing an alarm going off in the area, Cobb fire spokesman Dan Dupree said.

Dupree said police and firefighters arrived to find flames shooting through the roof of the building, which was not occupied when the fire broke out.

It took fire crews about 45 minutes to bring the flames under control, he said.

One firefighter suffered an ankle injury and was taken to a local hospital as a precaution, Dupree aid.

He said the cause of the fire has not been determined.