Police are diverting traffic off Puuhale Road in Kalihi after an explosion in a manhole.
Several hundred Hawaiian Electric Company customers were knocked off the power grid in connection with the incident.
Police said firefighters requested assistance after a blast was heard coming a manhole shortly before 10 a.m. A transformer apparently blew, causing the underground explosion, police said. No one was hurt.
Hawaiian Electric Company spokesman Darren Pai said about 300 hundred customers were left in the dark and troubleshooters were investigating.
Officers were diverting traffic near Puuhale and Democrat Street.