Six fire engines and around 40 firefighters attended a fire at a hotel on Prince's Square in Bayswater.
Part of a room in the basement of the building was damaged by fire. Around 140 people left the building before firefighters arrived and around five people were assessed at the scene by London Ambulance Service for smoke inhalation.
The fire is being treated as accidental and is believed to have been caused by the failure of a lithium-ion battery.
A London Fire Brigade spokesperson said: “Lithium batteries are susceptible to failure if incorrect chargers are used, so it’s important to always use the correct charger for the product and buy an official one from a reputable seller.
"You should unplug your charger when you have finished using it and we would advise not to leave it unattended or charging while people are asleep.
“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 too.
“Try to ensure they are not getting knocked around while in use or while being carried as this can increase the chance of damage to cells."
The Brigade was called at 1801 and Control Officers mobilised crews from Kensington, Paddington, North Kensington and Soho fire stations to the scene. The fire was brought under control by 1926.