A probe is under way after a huge fireball burst from a pavement on a busy street, narrowly missing a passer-by standing just yards from the blast.
The dramatic explosion was said to have shaken nearby buildings and left a gaping crater at the side of the road.
Video footage of the blast shows one astonished bystander running from the scene as flames shot from the ground.
The Health and Safety Executive (HSE) said it is looking into the explosion which is believed to have been caused by a fault on the underground electricity network on Thursday morning. Cables at that spot, on Pimlico Road in central London, carry up to 11,000 volts
Nearly 2,000 people in the area saw their power interrupted following the explosion.
Witness Charlie Brook described hearing three explosions. The most dramatic of these was the second blast which she filmed from her window. In the footage, a man can be seen talking on his mobile phone before flames erupt from the pavement and he is then seen running from the scene.
Ms Brook said: "It was frightening. The chap on the corner had a very lucky escape from the scene. It's a very busy street and anyone could have been walking past."
She added: "It's very lucky no-one was injured. My fear was that the explosions would travel. My main concern was the safety of residents."
A spokesman for UK Power Networks, which maintains the electricity distribution network in the region, said: "At 10.25am yesterday a fault on our underground electricity network in Pimlico Road interrupted power supplies to 1,867 customers. UK Power Networks engineers rerouted supplies to 861 customers within ten minutes and all supplies were reconnected by 1.55pm.
"Safety is our top priority and the cause of this incident is being investigated. We apologise to customers for the inconvenience caused by the power cut and our staff restored all supplies as quickly as safely possible."