An explosion which demolished a flat above a shop owned by property tycoon Leo Noé is being treated as suspicious.
Police said the cause of the blast, in Bell Lane, Hendon, was unknown and an investigation has begun.
A 39-year-old man, thought to live in the flat, suffered serious burns and remains in a critical condition in hospital.
An elderly woman, whose house backs onto the premises, suffered shock when her windows were blown out, and was treated at the scene.
A woman, aged 26, and a man, aged 31, also received treatment for minor injuries.
Detective Sergeant Mark Tyrrell of Barnet CID said: “The explosion and resulting fire caused massive damage to the premises and has affected properties in the surrounding area. It is a miracle that not more people were hurt as a result.
“Enquiries will continue at the scene to establish exactly what has happened and I would ask anyone with information to call police.”
Mr Noe was at a wedding in Hendon at the time, and when he heard about the explosion went to the site along with several other wedding guests who also had business interests in the area.
Members of the voluntary Jewish North West Community Patrol who had been patrolling the surrounding area were first on the scene.