A 25-year-old has been arrested over a high-speed crash on the M1 in which two people were killed and another six injured.
The man from east London is being held by Hertfordshire Police on suspicion of causing death by dangerous driving after the crash in the early hours of Monday morning.
Two BMWs collided on the M1 near Watford shortly before 2.40am, killing the driver and rear seat passenger of one of the cars.
Witness Basit Nasir told the Evening Standard that the BMWs "appeared to be having a high-speed race" and had sped past him at around 140mph.
He said: "It was total mayhem. There was mangled metal everywhere. It was foolish of them to drive at this sort of speed. It was raining as well."
Mr Nasir said that four men in a Mercedes arrived at the crash scene and scuffled with survivors.
He told the newspaper: "They all jumped out and everybody started punching each other. They said, 'What have you done? You have killed them.' I tried to break up the fight and called the police from my mobile."
The two men who died have not been named by police but were aged 22 and 24 and both from east London.
Two other passengers in the same car were also hurt and taken to St Mary's Hospital in Paddington, central London, with "serious injuries", Hertfordshire Police said.
Four men travelling in the other BMW also needed hospital treatment for their injuries.
The accident, which happened on the southbound section between junctions five and four, resulted in the closure of five junctions of the motorway in both directions, and the southbound stretch was shut for several hours.
Hertfordshire Police have appealed for witnesses to the crash or the events that led up to it to contact them.