Seven people were arrested after two vehicles traveling near the G7 summit were found to contain paint, smoke grenades and loud hailers, police said.
Devon and Cornwall Police confirmed that officers carried out a vehicle stop on a car and a van near Loggans Road in Hayle about seven miles from the Carbis Bay Hotel.
The force said during the stop, at about 5 p.m. (1500 GMT) on Thursday, the vehicles were searched and the items were found inside.
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.
Others arrested were 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.
A force spokesman said all seven remain in police custody.
He said: “The items and the vehicles have been seized by police as part of ongoing inquiries 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,” he added.