First-lap onboard footage appears to show that protesters accessed the track by the base of the bridge on the Wellington Straight, jumping the barrier on lap one as leader Max Verstappen passed.
But the race had been simultaneously red flagged for the huge Zhou Guanyu crash at the opening turn, which sent the Alfa Romeo driver rolling over the barrier.
At least five people were pictured sitting on the asphalt before marshals began to clear the protesters, with the Just Stop Oil climate activist group soon claiming responsibility.
Northamptonshire police has now issued a statement and revealed that seven people have been arrested for their "incredibly dangerous decision".
Event commander chief inspector Tom Thompson said: "I'm really disappointed that this group of people ignored our warnings prior to race day and made the incredibly dangerous decision to enter the track.
"We offered to facilitate a peaceful event at the circuit, but they instead chose to put the lives of the drivers, marshals and volunteers at risk.
"It is incredibly disappointing that anyone would make the decision to do this.
This demonstration arrived after Northamptonshire Police, who acknowledged protesting is "everyone's human right" received "credible intelligence" on Friday that some were planning to interrupt but urged anyone involved to not create excessive risk by "jeopardising lives"."
Thompson continued: "Thankfully we had plans in place for an eventuality such as this and the group were swiftly removed and arrested by our officers.
"All seven are currently in custody where their details are being ascertained.
"Finally, I would like to thank all of the officers and staff, as well as our partners, who have worked tirelessly on this policing operation.
"Generally, we have had very low crime rates, today's incident was dealt with effectively and efficiently, and I could not have asked for more."
Asked by Autosport for his account, McLaren driver Lando Norris labelled it "worrying".
"If you've really got to be that silly to go on to a race track with Formula 1 cars… it's a scary thing," he said.
"At the same time, you're putting us at risk to be involved in something that we would never ever want to be involved in.
"I'm sure the track did as much as they could to stop it."
