Vin Diesel is said to be "tearful" and in "total shock" after seeing his Fast & Furious 9 stunt double plunge 30ft from a balcony.
The stuntman was airlifted to hospital after the accident, which is feared to have been caused by a snapped cable.
It's said the man, whose identity is not known, suffered serious head injuries as he hit the ground.
Vin, 52, who plays Dominic Toretto in the movies, was left in shock after the accident at Warner Bros studios in Levesden, Herts.
Filming was immediately halted and the cast and crew were sent home "fearing the worst" as the stunt double was taken to Royal London Hospital.
A source told The Sun : "The stuntman fell at least 30ft - maybe a bit more. Vin Diesel was seen on set seconds after. He looked ashen, totally in shock and blinking back tears. He saw what happened."
The unnamed man is thought to have been acting as Vin's stunt double in the new movie.
The accident happened just before midday on Monday, and police confirmed they attended the scene to carry out inquiries.
The source added: "They were filming a very high balcony scene. The stuntman leapt from the balcony attached to a safety wire, but it looks like the cable snapped.
"He was meant to be left dangling below the balcony via the wire and then lowered slowly to the ground, but he plunged to the ground and landed on his head."
The insider said there were "gasps" and "screams" as the man hit the floor, and that the horrifying accident was caught on camera, with the footage being handed to police.
They added that the brand new set has now been closed down and is considered a "crime scene".
Vin has suffered a lot of heartache throughout his career.
His stunt double on 2002 movie xXx, Harry O'Connor, was killed in an accident while filming a para-sailing scene.
In 2013, his Fast & Furious co-star Paul Walker was killed in a car crash during filming of the seventh film. He was 40.
Mirror Online has contacted Vin's representatives for comment.
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