Firefighters were called to a suspected carbon monoxide leak at a pub and hotel on Hereford Road in Bayswater.
Crews used specialist equipment to confirm elevated readings of carbon monoxide on arrival. Around 100 people left the building before the Brigade arrived and a woman was taken to hospital.
The gas supply was isolated and crews ventilated the property and carried out a sweep of the building to confirm no elevated readings remained.
A London Fire Brigade spokesperson said: “You can't taste, see or smell CO fumes, but it can kill in minutes.
"It's really important to fit a CO alarm in all rooms containing fuel burning appliances, ensuring that the alarm is able to be heard throughout your home. When sleeping, it is important that your alarm would wake you if it sounds.
"It’s also a good idea to familiarise yourself with the signs of carbon monoxide poisoning and learn what to do if you suspect someone may be affected.”
The Brigade was called at 2157 and the fire was under control by 0056. Fire crews from North Kensington and Kensington fire stations attended the scene.
CO poisoning symptoms:
These symptoms also apply to your pets – so keep an eye on them too. Poisoning symptoms can easily be confused with just feeling unwell, which is why CO poisoning is so dangerous, and so often missed