After Red Bull driver Max Verstappen crossed the line eight seconds ahead of McLaren's Lando Norris to win the 71-lap race, "a large group" of spectators made their way onto the circuit.
This occurred at Turn 1 during the chequered flag lap while cars were still on track. Although there were no injuries, the stewards summoned race officials due to serious safety concerns.
There is an agreed time at which the gates open to allow fans onto the track so that many may make their way to the main straight for the podium ceremony.
Motorsport.com understands that at Interlagos, people climbed over the fences while the circuit was still classed as live.
After reviewing CCTV evidence and hearing from race organisers, the FIA has ruled that any measures were "not enforced and/or were not sufficient resulting in an unsafe environment".
The governing body noted: "[Organisers] candidly admitted the failures in terms of the security protocols and safety measures.
"[They] concurred with the FIA Sporting Delegate and the Race Director report and agreed that comparable circumstances already occurred in Brazil and that this was an unacceptable situation which could have had disastrous consequences."
In line with a similar incident at the end of the 2023 Australian GP, when Nico Hulkenberg's car was also on track in an unsafe condition due to having possible electrical discharge, Brazilian GP officials must conduct a thorough investigation and take remedial action in time for the 2024 race.
By 30 January 2024, race organisers must "present a formal remediation plan to the FIA that adequately addresses the serious concerns".
The stewards have asked the FIA to review the measures agreed to and the World Motor Sport Council can apply further penalties. However, the Australian GP did not face further sanctions.
A record-breaking, sold-out crowd of 267,000 people attended the Interlagos circuit over the weekend.
Earlier this weekend, it was announced that the Brazilian GP has agreed a five-year contract extension that, added to its existing deal, will keep the race on the F1 calendar until the 2030 season.
