GARDEN GROVE, Calif. (KABC) -- Firefighters battled a four-alarm building fire that erupted in a Garden Grove restaurant early Wednesday morning.The fire started around 3 a.m. at a strip mall in the 12000 block of Brookhurst Street. It was unclear what caused the fire, but it was quickly upgraded from a second-alarm to a four-alarm blaze within an hour.More than 70 firefighters were on scene trying to quell the flames. The area between Lampson and Chapman avenues was closed.The cause of the fire was unknown. No further information was immediately available.