The anti-government protesters drowned out about 40 supporters of President Ali Abdullah Saleh at Sanaa University, where the march began, CNN and China's state-run Xinhua news agency reported.
After the initial demonstration, some young protesters marched on the presidential palace. At barricades two miles away, they battled security forces, some armed with stun guns, witnesses told The New York Times. Several injuries but no deaths were reported.
Inspired by the Egyptian revolution, the demonstrators chanted, "First Mubarak, now Ali," CNN reported.
Saleh, who has ruled for 32 years, amended the Constitution to make him leader for life and pass on the title to his son, but on Feb. 2, he announced he would rescind those measures as unrest spread, Xinhua said.
Sunday, the main opposition party issued a statement Sunday saying it would accept Saleh's changes, Xinhua reported.
"We have frozen all opposition protest against the regime," the statement said. "But we call on President Saleh and his ruling party to keep all their commitments and absorb the lessons from the uprisings in Tunisia and Egypt."
But youthful protesters seemed unwilling to compromise.
A coalition of opposition parties said Sunday it welcomed the new protests but cautioned that mass uprisings in Yemen, a country with a well-armed populace, could turn violent.