Australian Grand Prix organisers have promised to investigate after fans invaded the track before Sunday’s race had officially finished.

Some reached the stranded Haas of Nico Hulkenberg on the exit of turn two.

The sport’s governing body, the FIA, said the incident was a serious breach of the sporting code.

Australian Grand Prix Corporation chief executive Andrew Westacott said the outcome at Melbourne’s Albert Park “could have been horrific”.

The FIA said “security measures and the protocols which were expected to be in place for the event were not enforced resulting in an unsafe environment for the spectators, drivers and race officials”.

It has demanded that organisers “urgently present a formal remediation plan”.

Westacott said officials would trawl security cameras to try and find out how the breach occurred at the end of an incident-packed race which was won by Red Bull’s Max Verstappen and ended under a safety car after a crash-affected restart.

“There’s a controlled allowance of people to come on to the track after the race has concluded and after the safety car passes,” he told ABC.

“Spectators had broken one of the lines, we don’t know how that’s occurred just yet.

“We’ve got a lot of CCTV and we’ve got a huge amount of footage we’re going to have to pour through over the next couple of weeks.

“Motorsport is dangerous – it could have been horrific.

“Nobody does anything malicious at motorsport, it’s an unbelievably well-behaved crowd but they, I think, had a degree of confusion. We don’t know how they got into the area without the right level of authority.”

Meanwhile, race organisers have also been criticised by a spectator who suffered a cut to his arm when he was struck by a piece of debris from Haas driver Kevin Magnussen’s car.

Will Sweet told Australian radio station 3AW he was standing with his fiancee on a packed hill just off turn two when the Dane’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 fiancee, 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.”

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.