Four people have been hurt in a blast at a block of flats on Wednesday morning in Wandsworth, south London.
An elderly man in his seventies has been taken to hospital and three others were treated at the scene for minor injuries, according to the Metropolitan Police.
Police, fire and ambulance crews attended to find a wall damaged and are working to assist those who were injured as a result.
London Fire Brigade said the cause is not yet known and police have not made any arrests.
Metropolitan Police Sergeant John Nicolaou said: "We now know four people have been injured as a result of what is believed to be a gas explosion.
"Three of those were treated at the scene for minor injuries. An elderly man has been taken to hospital for treatment."
He said the Gas Board is investigating the cause of the blast.
A spokeswoman for London Fire Brigade said: "Four fire engines and around 25 firefighters have been called to a suspected gas explosion on Garratt Lane in Wandsworth.
"Firefighters rescued one man from the affected flat. He has been taken to hospital. A man from an adjacent flat left before the brigade arrived and has also been taken to hospital."
A 25m cordon has been put in place as a precaution and motorists have been told to avoid the area.