Update at 1:05 p.m.: Power has been restored to the Back Bay and surrounding areas, according to a mayoral aide speaking at the Scotia Street substation.
NStar said nearly 13,00 customers lost power for almost an hour.
NStar is asking any customers still with a power outage to call the utility directly at 1-800-592-2000.
As we reported earlier, the outage stemmed from the same substation that had a fire in March, causing a widespread blackout.
Update at 3 p.m.: NStar said in a statement: "The exact cause of the outage is under investigation, however we can confirm that there was no damage to any electrical components, that’s why we were able to restore power in such a short amount of time."
It added: "Since the March 13th transformer fire in the Scotia Street substation, crews have been working around the clock to replace the transformer, make repairs, and put in additional contingencies to help provide added redundancies in the downtown Boston power network."
Update at 12:51 p.m.: Massachusetts State Police said the Prudential Tunnel's lights and vents are currently running on a generator.
Update at 12:35 p.m.: NStar said it is not immediately sure what may have happened to cause the outage.
With many traffic and street lights out, Boston Police have encouraged motorists and pedestrians to use caution. Officers have been deployed to the area to assist with traffic.
Update at 12:24 p.m.: The MBTA tweets that Green Line service is not affected by the power outage, but that elevators are out of service at Prudential station.
The utility NStar is reporting a power outage in the area of Boston's Back Bay, according to the city.
There are reports that the outage is affecting Kenmore Square and Boylston, Clarendon and Marlborough streets, among other city locations.
No further information is immediately available on the outage.
In March, a smoky transformer fire caused a widespread blackout in the Back Bay, leaving more than 20,000 customers in the dark, including the Prudential Tower.
We'll have more as this story develops.
This program aired on May 8, 2012. The audio for this program is not available.