Thousands of Long Beach customers were without power Wednesday after an underground electrical fire downtown that caused manhole covers to blow off, forcing police to close several streets.

City News Service reported that The Aquarium of the Pacific in Long Beach closed Wednesday afternoon due to the power outage affecting an estimated 4,000 customers south of Ocean Boulevard, according to Southern California Edison.

Long Beach police, however, indicated the outage area was much larger, from Seventh Street south to the waterfront between Magnolia and Alamitos avenues. The outages were expected to last for several hours into the night, police said.

An SCE spokeswoman said the number of affected customers increased because workers had to shut down equipment in the area to keep people safe.

Police initially asked residents to stay indoors and closed from Daisy to Cedar avenues and from Ocean Boulevard to Fifth Street. Smoke could be seen billowing from underground, through manholes in the downtown area. The cause of the fire is under investigation.

• Video: Smoke comes from a manhole cover at Third Street and Magnolia Avenue

The power outage was initially reported at 3:08 p.m. Wednesday. A spokesman from Southern California Edison, David Song, said officials don’t know the cause but are investigating.

“The situation is still evolving,” Song said.