Will Sweet told Australian radio station 3AW he was standing with his fiancée on a packed hill just off turn two at Albert Park during Sunday’s race when the Danish Haas driver’s car hit the track-side barrier sending his tyre and debris flying into the air.

“It slapped me in the arm and I was just standing there bleeding,” he said.

“My arm was covering where my neck would’ve been, but if that had hit my fiancée, it would’ve got her right in the head.

“I realised how big it was and how heavy it was. Part of it was shredded and really sharp, if it hit me in a different angle, it could’ve been horrendous,” he added.

Australian media published a picture of Sweet holding a large piece of debris with blood trickling down his forearm and another showing him having treatment from a medical official at the track.

Sweet said the area he was standing was packed, with young children around, and that no race officials came to assist him.

“No one even came and looked,” he said.

“My fiancée was pretty spooked by it and borderline shell-shocked.”

The race’s organisers are already under scrutiny after a large number of fans invaded the track near the end of the race.

Late on Sunday, Formula One stewards ordered the Australian Grand Prix Corporation (AGPC) to urgently produce a “remediation plan” in response to security and safety failures that allowed fans to access the track.

Sweet said debris from Magnussen’s car had flown “straight up, way over the fence” and into the crowd.

The AGPC did not provide immediate comment.

At the 2001 Australian Grand Prix, a track marshal was killed when hit by the wheel of Jacques Villeneuve’s car following a crash with Williams’ Ralf Schumacher.

Organisers said a crowd of 131,124 attended Albert Park on Sunday and a record total of 444,631 spectators across the race week.