Four men had to be dragged from a wrecked car by passers-by just moments before it burst into a fireball and was completely destroyed.
The Met Police said the black Volkswagen Golf smashed into a wall at Northwick Park roundabout in Harrow, north west London just before 5am on Wednesday before it was engulfed by fire.
The driver and three passengers were all saved from the blaze by members of the public, Scotland Yard said.
Two are still in hospital - a 29-year-old is in a critical condition with head and neck injuries, while a 27-year-old suffered internal injuries and is in a stable condition.
The other two men caught up in the smash, aged 22 and 29, were treated for minor injuries.
Officers said want to speak to witnesses, particularly a man who filmed the aftermath of the crash on his phone. Scotland Yard said the footage could prove "vital".
Anyone with information can call police on 020 8991 9555.