An electricity sub-station “exploded” yards from a children’s play area in Hendon.
Witnesses said they heard an almighty bang when the substation on the Belle Vue Estate underwent a power surge on Sunday at 7.50am.
The explosion caused a partial collapse to the surrounding brick building and a small fire started in the roof.
Firefighters were called to Bell Lane to tackle the flames, which were already extinguished when they arrived.
Back-up generators kicked in to prevent a loss of electricity on Sunday but thousands of homes were briefly affected this morning when engineers from UK Power Networks went to inspect the problem.
Roy Dunn, 67, lives in a flat yards away from the sub-station. He said children regularly use the walls of the brick building as a goal when playing football.
The former caretaker said: “It’s lucky no-one was next to it at the time. I was sitting in the lounge with my wife when we heard this huge bang. It sounded like an industrial container being dropped.
“I looked outside and there were flames and thick black smoke pouring out of the substation and the building had partially collapsed.
“It was a bit of a shock seeing how much damage it had done. You’re naturally worried that it was something deliberate but we don’t really get things like that around here. We phoned the fire brigade and they were here pretty quick.”
UK Power Networks, which owns the substation, blamed faulty equipment for the explosion and said a full investigation is underway.
A spokesman said in a statement: “In order to safely carry out repairs to the substation we reconfigured the electricity network earlier today and this work interrupted power supplies to several thousand customers at 9.44am.
“The first supplies were reconnected within a few minutes and all supplies were reconnected by 10.10am. We would like to apologise to customers for the inconvenience caused.”