About 1,000 people had gathered in the southern Italian town of Giardini Naxos for the rally in Sicily on Saturday.
Prior to the tear gas incident, organizers insisted that their aim was to conduct a peaceful demonstration.
Organizers had expected more than 3,000 people to attend the “No G7” rally, which was to focus on issues including migration, free trade and global warming.
“This is not about violence,” said Gianmarco Catalano, one of the organizers, prior to the protest. Catalano insisted that one of the aims was to raise issues that are not on the agenda at the summit such as human rights.
Shop and cafe owners along the beach promenade in Giardini Naxos had barricaded up their businesses by midday.
On Friday, Greenpeace organized a protest centered around a model of the Statue of Liberty clad in a life jacket on the Taormina beach. The group called for the Paris Climate Agreement to be implemented without delay.
“The G7 countries have largely caused the climate change problem, now they must tackle the solution,” Greenpeace Germany Director Sweelin Heuss said.
Oxfam called on the G7 to take concrete steps to ease the refugee crisis, arguing that the dignity and rights of refugees had to be respected.
In the past, G7 and G20 protests have been accompanied by violence, even though the protesters are kept well away from the summit venue.
Weeks ahead of the Sicily summit, Italian security officials began conducting checks to remove potentially violent protestors.