Seven people equipped with paint and smoke grenades have been arrested just 10 minutes away from the G7 summit.
The group were stopped by police in Hayle, Cornwall, at around 5pm on Thursday, police said.
The town is less than four miles from Carbis Bay, where world leaders are meeting this week.
Officers carried out a search of a car and van and discovered several items, including loud hailers.
It is understood that the incident relates to a planned protest over the G7 event.
Three people were arrested on suspicion of possessing an article with intent to commit criminal damage.
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The group were stopped near Loggans Road in Hayle, Cornwall
Four others were arrested on suspicion of conspiracy to commit public nuisance, Devon and Cornwall Police said.
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 event is taking place in Carbis Bay
(Image: AFP via Getty Images)
"They remain in police custody at this time.
"The items and the vehicles have been seized by police as part of ongoing enquiries in relation to this matter.
"We continue to support the facilitation of safe and legal protest but criminal activity and public disorder will not be tolerated."
The summit is being attended by numerous political figures, including Boris Johnson and US president Joe Biden.
It is the first in-person meeting of the leaders of major developed economies for nearly two years.
World leaders including Joe Biden and Boris Johnson are attending the event
(Image: Andrew Parsons / No10 Downing Street)
The Prime Minister said he plans to use the event to urge the members – also including Canada, Japan, France, Germany and Italy – to "defeat" Covid-19 by helping to vaccinate the world by the end of next year.
Protesters said previously 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, one of about 20 activist organisations to have joined a 'Resist G7 Coalition'.
Extinction Rebellion, which caused traffic chaos in central London with 11 days of protests in 2019, has said it expects some 1,000 protesters to make their way to St Ives, a nearby town, for the summit.
Police have closed off roads and coastal paths to Carbis Bay, erecting steel fences and putting other restrictions in place.
An extra 5,000 officers have been drafted in to help the operation, with about 6,500 officers and staff involved altogether.