Two fire engines and around ten firefighters attended a carbon monoxide leak at a hotel on Tavistock Place in Bloomsbury.
Around seventeen people were evacuated from a four-storey mid-terraced hotel by firefighters wearing breathing apparatus. One man, one woman and two children suffering from the effects of carbon monoxide inhalation were to taken to hospital.
The Brigade was called at 0629 and the incident was under control at 0828. Fire crews from Euston and Soho fire stations were in attendance.
The cause of the leak is under investigation.