A manhole cover was blasted into the air on Tuesday night as flames emerged from an underground electrical cable.
The explosion took place in Chancel Street – close to the Edward Edwards House sheltered housing complex and Transport for London's taxi and private hire test centre – at about 6pm on Tuesday.
Engineers from UK Power Networks were already working in the adjacent electrical substation investigating a fault that had been reported earlier that afternoon
No-one was injured in the explosion but one passer-by was hit by flying debris.
"A fault occurred on an underground electricity cable affecting the local area," said UK Power Networks.