While May Day labour protests in Canada were largely peaceful, a Vancouver family had its car smashed during a Seattle riot, according to U.S. media reports Tuesday.

A man, identified only as Sam, told reporters he was on holiday with his family, and was returning to his parked Hyundai outside Niketown when his B.C. plates attracted the mob. His car's windows were smashed, while nearby police looked on.

"I don't know why people want pictures of my car. I don't know why they have to mouth off to me and tell me to go back to Canada," he told Seattle media. "This is a real welcome to Seattle."

A Kiro TV reporter described the scene in his live report, "As he's here returning to the car . he starts getting heat from people on bikes riding by him. They had seen the British Columbia licence plate. They started saying, 'Hey hoser, go back to Canada.' I kid you not, he was getting grief from people . for being from Canada."

Hours later, Seattle Mayor Mike McGinn apologized and said at least two people have been arrested. He signed an emergency order to allow police to seize items that could be potentially used as weapons, particularly tire irons, sign posts, and hammers.

According to officials, similar outbursts also hit Oakland, Portland and San Francisco.

In Vancouver, a crowd of about 200 turned up at Vancouver Art Gallery, including members of different unions, Occupy Vancouver, and others themselves as communists, socialists and anarchists.

Some shouting and pushing broke out between some Occupy speakers over allegations one member of the movement had been stalking another. The tension was diffused with minimal police involvement.

Paul Finch, B.C. Government and Services Employees' Union president, wasn't surprised by the Occupiers presence.

"In Canada, and other countries, the GPD is growing year after year. But at the same time, the growing contradiction between rich and poor is becoming more disparate."

All was quiet late Tuesday afternoon at press time, but the Vancouver event was expected to run into the night.

-with files from Byron Chu