Sections of Boston that lost power because of a smoky electrical transformer fire are slowly recovering but problems are expected to persist for most of the day.

The fire, in a 115,000-volt transformer, was reported at about 6:30 p.m. Tuesday and knocked out power to about 21,000 homes and businesses.

About 8,000 of those customers had power by Wednesday morning, but with traffic lights and other road signals still out, police are expecting problems with the morning commute. An NStar spokeswoman says the utility is bringing in generators and hopes to have power back to everyone by Wednesday evening.

The Prudential Tunnel on the Massachusetts Turnpike was closed, but reopened on Wednesday morning.

Two subway stops in the area remained closed.

Police are advising people to stay away from the area. (AP)