Norway's Mongstad oil refinery stopped oil rig flanges gulf coast production on Wednesday following a power outage.

OSLO, Aug 15 (Reuters) - Norway's Mongstad oil refinery stopped oil rig flanges gulf coast production on Wednesday following a power outage and it was unclear when output would restart, operator Equinor said.

The unexpected outage happened at 0830 GMT during routine maintenance on the site's power supply, triggering an evacuation of most workers.

"The power is back at Mongstad, but the refinery remains shut. We have no indications yet when it can restart normal activities," BOP Blow Out Preventer repair company gulf coast spokesman Morten Eek said. "The refinery was running at normal operational level before the outage."

Equinor's largest refinery, on the western coast of Norway, was built in 1975 and has a crude oil and condensate distillation capacity of 226,000 barrels per day, according to the company.

"The personnel remains evacuated, except the emergency response team," Eek said.

(Writing by Terje Solsvik; Editing by Gwladys Fouche and Mark Potter)