A gathering of about 3,000 people shut down a stretch of the U.S.-Canadian border for more than four hours Saturday in the largest of several American demonstrations against the free trade summit in Quebec. 

In San Diego, about 1,000 people demonstrated at the U.S.-Mexican border. Some participants in a demonstration of about 400 people briefly blocked traffic near the entrance of the tunnel that links Detroit and Windsor, Ontario. And in Vermont, about 200 people rallied. 

The protest in Blaine, a town of about 3,800, remained peaceful as demonstrators chanted, gave speeches and sang songs against the Summit of the Americas, where representatives from 34 countries were negotiating a Free Trade Area of the Americas. 

Canadian and U.S. authorities closed the border so no one would be hurt, Cpl. Janice Armstrong of the Canadian police said. She praised the organizers for a "very peaceful, well planned and well organized" demonstration. 

Eight people — all believed to be Canadian citizens — were arrested and taken to Surrey, British Columbia, for processing. They face Canadian charges of participating in an unlawful assembly. 

The rally at the U.S.-Mexico border resulted in a 20-minute standoff between rock-throwing protesters and police in riot gear, but there were no injuries or arrests, police said. 

Several dozen people in Detroit blocked traffic near the tunnel entrance for about 20 minutes in a show of support for demonstrators at the Summit of the Americas. No arrests were made. 

Protestors also rallied at border crossings in Derby Line, Vt. and across the state in Highgate Saturday.