Another vehicle blasted techno-disco music into the cheering Romney crowd.

Comparatively small enclaves of demonstrators for Libertarian candidate Carla Howell and the Green Party’s Jill E. Stein ’73 moved among the pro-Romney and pro-O’Brien crowds.

At one point, Howell and Stein, who were not participating in the evening’s debates, appeared and spoke in huddled crowds of supporters.

“I’m here to support Jill and free choice. It’s really great to have another option,” said Ian P. Tosh, who was demonstrating for the Green candidate. “It’s an opportunity to make a statement with your vote.”

Advocates of non-gubernatorial political priorities were also present at the demonstration. A group of young adults representing the Campaign for Tobacco-free Kids Action Fund distributed fliers to passers-by.

The present governor cut funding for the Massachusetts Tobacco Prevention Program by 90 percent, they said, and their campaign seeks to reinstate full financial support.

“We are trying to get it back because it saves money in the long run,” said Thady J. Sweeney, one of the group’s members.

A man wearing a “Save Jesus” poster around his neck also wandered among the crowd distributing pamphlets.

Police officers had sectioned off the leftmost lane of Tremont Street for demonstrators, and they controlled the narrow stream of traffic on the remaining lanes.

The smallest group of demonstrators carried mock signs favoring “Governor Steve Sweeney.” Sweeney is a morning host on Boston’s WZLX radio station.

Asked about this humorous political statement, Jared Frontiero, a Sweeney campaigner, grinned.

“A vote for Steve is a vote for something,” he said.