The group were stopped and their two vehicles searched in Hayle at around 5pm on Thursday, according to a statement issued by Devon and Cornwall Police.
As well as paint and smoke grenades, loud hailers were discovered in the vehicles. Police arrested three on suspicion of possession of an article with intent to commit criminal damage, and four on suspicion of conspiracy to commit public nuisance.
A statement said: “A search was carried out on the vehicles which were found to contain items including paint, smoke grenades and loud hailers.
“A 30-year-old man from London, a 21-year-old woman from Wales, and a 20-year-old man from Bournemouth were arrested on suspicion of possession of an article with intent to commit criminal damage.
“Two men from London aged 25 and 27, a 45-year-old woman from London and a 26-year-old woman from Epsom were arrested on suspicion of conspiracy to commit public nuisance.”
The force said they remain in police custody and their property has been seized as part of ongoing police enquiries.
“We continue to support the facilitation of safe and legal protest but criminal activity and public disorder will not be tolerated,” police said.
A group of around 20 activist organisations has formed a ‘Resist G7 Coalition’ to protest at the G7 summit, with demonstrators previously saying that they intended to be “noisy, disruptive and annoying”.
“Our rights weren’t won through quiet, polite protest. Our rights were won through being noisy, disruptive and annoying,” said the Kill The Bill group, which is campaigning against proposed legislation to grant police further powers to curb protests.
Activists from local Extinction Rebellion groups are also voicing their concerns at the summit, calling for world leaders to take stronger action to tackle the climate emergency.
The protests come as Boris Johnson defended taking a private plane rather a train to get to the summit, where climate change will be a key focus. Flying creates almost five times the amount of emissions compared to the equivalent train journey, according to the government’s own emission figures.
A statement on the coalition’s website reads: “We believe in a world where we put people and planet before profit, where justice means justice on a global scale, where wealth is shared equally and not pocketed by the 1 per cent.
“Our world should not be a play thing for the rich. It belongs to all of us. And it’s down to us, the people, to stand together, to resist, and to create the future we want to see. The world leaders at the G7 aren’t going to do it for us. The system needs changing. And if we want change, we have to act.”
Some 5,000 extra officers have been brought in to police the event.