Four fire engines and around 25 firefighters tackled a fire at an office building on Fenchurch Street in the City of London.
A small part of a cloakroom on the seventh floor of the building was damaged by fire. There were no reports of any injuries.
The fire is believed to have been accidental and caused by the failure of a lithium battery power bank.
A London Fire Brigade spokesperson said: “Batteries can present a fire risk if they’re over-charged, short circuited, submerged in water or damaged, so it’s really important to protect them against being damaged and charge them carefully.
“Try to ensure they are not getting knocked around while in use or while being carried as spares as this can increase the chance of damage to cells.”
The Brigade was called at 2247 and the fire was under control by 0052. Fire crews from Dowgate, Whitechapel, Dockhead and Shadwell fire stations attended the scene.