BANGOR, Maine — Power has been restored to all but one building after a section of downtown Bangor went dark around 3:45 p.m. Monday when a transformer exploded underground in the vicinity of Mexicali Blues in West Market Square.

“We just heard an explosion downstairs and then the lights went out,” said Stephanie White, a 23-year-old store employee. White and a co-worker, Heidi Lynch, stood on the sidewalk outside the business as firefighters arrived.

They said the noise was “terrifying” and startled everyone in the building. White and Lynch made sure employees and a few customers who were inside at the time of the incident left the building.

Firefighters were at Mexicali Blues minutes later assessing the damage and using fans to ventilate the building.

It’s unclear how much of downtown Bangor lost power, but the bulk of outages seemed to be in the downtown area around West Market Square. Emera Maine reported about 320 customers without power around 4 p.m.

Power was restored to all but the Mexicali Blues building shortly before 4:30 p.m., according to Emera Maine spokesman Bob Potts. He said it was not yet clear when power would return to Mexicali Blues.

Soon after, Emera’s online outage map reported no customer outages.