The chief of the Australian Grand Prix vowed a full investigation on Monday after fans invaded the track before the race had officially finished, saying the outcome "could have been horrific".
The sport's governing body, FIA, summoned organizers for an explanation late Sunday after the race, ruling the invasion a serious breach of the sporting code and demanding they "urgently present a formal remediation plan".
Footage showed a "large group" of the 131,000-strong crowd squeezing through barriers and climbing fences just meters from speeding cars near the conclusion of a drama-packed race won by Red Bull's Max Verstappen.
Some were able to reach the stranded Haas of Nico Hulkenberg, which parked on the exit of Turn 2 after finishing seventh.
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".
Australian Grand Prix Corporation boss Andrew Westacott said organizers were still not sure what happened, but admitted it was unacceptable.
"There's a controlled allowance of people to come onto the track after the race has concluded and after the safety car passes," he told national broadcaster ABC.
"Spectators had broken one of the lines, we don't know how that's occurred just yet."
Westacott said officials would trawl security cameras to try and find out how the breach occurred.
"We've got a lot of CCTV and we've got a huge amount of footage we're going to have to pore through over the next couple of weeks," he said. "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."
Verstappen's win, after the race was red flagged three times, extended his lead over teammate Sergio Perez in the world championship to 15 points after three grand prix.
Red Bull lead the constructors standings by 58 points ahead of Aston Martin, with Mercedes third.
