Vin Diesel is in 'total shock' after witnessing his stunt double plunging 30ft while filming for Fast and Furious 9 as crew members fear the worst.
The unnamed crew member is battling a serious head injury after the accident on the Hertfordshire film set.
Diesel, 52, was ashen-faced and tearful following yesterday's horrific fall, a source told The Sun Online.
'The stuntman fell at least 30ft — maybe a bit more,' the source said. 'Vin Diesel was seen on set seconds after. He looked ashen, totally in shock and blinking back tears. He saw what happened.'
Warner Bros Studios confirmed that a man had been airlifted to Royal London Hospital after MailOnline revealed an accident had taken place.
Producers told Deadline that the fall occurred just before noon on set in Leavesden during filming of Fast & Furious 9, which is set to feature stars such as Michelle Rodriguez and Helen Mirren.
A spokesman for East of England Ambulance Service told MailOnline: 'An ambulance, three ambulance officer vehicles and Essex and Herts Air Ambulance were called to Leavesden Studios shortly before midday today, following reports of a man injured in a fall.
'One patient with a serious head injury was transported to the Royal London Hospital by air ambulance.'
In a statement, Hertfordshire Police added: 'Police were called shortly before noon today following an incident at Warner Bros Studios in Leavesden, Hertfordshire.
'It was reported that a man had been injured while working at the location and sustained serious injuries.
'The air ambulance attended and police officers are currently on scene to assist and carry out initial enquiries.'
Today's incident comes a month after a crew worker was slashed in the throat with a Stanley knife on the set of The Witches, which is being filmed at the same studio.
The scrap between a rigger and the stage hand, who had worked together previously, took place as around 100 crew in total were on set.
Meanwhile, it was reported last week how a worker found a shard of glass in a half-eaten muffin left by a customer at the Harry Potter Studio Tour, which is also based at Leavesden.
Staff then launched an internal investigation which found silver metal pins had been placed in a further 13 muffins.
Nearly six years ago, Fast & Furious star Paul Walker died in a high-speed car crash along with friend Roger Rodas in 2013.