The Met Police said one man had been left with minor wounds after a little “power organize blast” at around 19:00 BST.
A police cordon was set up blocking movement and part of the asphalt, however has since been lifted.
Onlookers portrayed “shouting, crying and yelling” after a noisy blast, trailed by “warmth and light” originating from a container of electrical wires.
Bronte Aurell tweeted: “I saw the blast on #oxfordstreet I was in that spot – if that is an electrical blast I would prefer not to ever meet one again. Was enormous!”
Adam Jogee tweeted: “Startling couple of minutes in John Lewis on Oxford Street. Blast and bunches of shouting, crying and yelling. On the whole to stow away or get out.”
Twitter account @Londonstuff tweeted a video demonstrating a lot of smoke saying: “Something’s occurred on Oxford Street. Individuals fleeing rapidly and freezing.”
A representative from the Met affirmed streets had now revived and crisis groups had remained down.
She said the power organization was at the scene.