UPDATE: 11:30 p.m.
Power has been restored to nearly all Tewksbury customers impacted by this evening's outage. Only small, scattered pockets remain in the dark.
More than 9,000 National Grid customers were without power Sunday night, including nearly 5,000 in Tewksbury.
The outages, which spread into sections of Wilmington and Andover, were triggered by a transformer fire on Route 38 near the Knights of Columbus.
Power went out just after 8 p.m.
Tewksbury Firefighters and National Grid crews responded to the scene.
There is no immediate word on when power will be restored.