Crews responded overnight to a report of manhole fires near Faneuil Hall in downtown Boston and remained on scene Sunday morning.
Eversource says the smoking manholes at Union and North streets were caused by an underground equipment failure that burned cables.
The Boston Fire Department and Eversource are working to fix the problem. No injuries have been reported and officials say there's no danger to the public.
About 20 utility customers, most of them commercial businesses, are without power Sunday morning.
Union and Clinton streets are closed for the time being. While Boston police are assisting with traffic, they say they do not believe there will be much of a traffic impact.
This is the second time this week that Boston firefighters have responded to manhole fires in the city. There was a similar situation Monday in downtown Boston that Eversource said was caused by a ventilation fan in one of the manholes that had caught fire.
Officials are looking into both of these situations.