Honolulu firefighters responded to an early morning fire that broke out at the H-Power plant at Campbell Industrial Park.

Capt. Jeffrey Roache, spokesman of the Honolulu Fire Department, said workers observed smoke emanating from the fourth floor of a building at about 3:05 a.m. today.

Approximately 40 firefighters responded and observed personnel battling the blaze.

Firefighters brought the fire under control at 3:35 a.m. and extinguished it at 4:14 a.m.

No injuries were reported.

The cause of the fire is under investigation.