An "electrical explosion" in a busy thoroughfare in central London during rush hour on Thursday caused panic among passersby and left one man slightly injured.
The blast in Oxford Street, a tourist magnet and one of the most visited shopping streets in Europe, took place at about 19:00 BST, causing pedestrians to rush for cover, local media reported.
Police cordoned off a stretch of the pavement and blocked traffic, but the measures have since been lifted.
"We're dealing with a small 'power network explosion' at 7pm in Oxford St, W1," the Metropolitan Police said on Twitter.
Images on social media have shown a blackened pavement and smoke rising from the street.
The BBC quoted eyewitnesses as saying they heard "screaming, crying and shouting" after a ringing blast.