ZANZIBAR (Reuters) - Security forces used tear gas, water cannons and sticks to disperse taunting opposition supporters in Zanzibar on Monday in a second day of violence over an election on the semi-autonomous Tanzanian islands.

The opposition Civic United Front (CUF) said that with more than two-thirds of votes counted, it had 54.2 percent versus 45.7 percent for the government, in power for the last four decades both on the islands and on mainland Tanzania.

But the ruling Chama Cha Mapinduzi (CCM or "Party of the Revolution") said it had taken the first seven of 50 legislative constituencies being fought and was on course for victory after Sunday's presidential and parliamentary poll.

Opposition supporters took to the streets of historic Stone Town, Zanzibar's main population center, from daybreak, dancing, singing and banging drums to proclaim victory.

But the situation quickly degenerated into a running battle, with police and soldiers firing tear gas into narrow alleys where youths taunted them and threw stones.

Reuters reporters saw about 20 people bundled into vans and taken away, some beaten in full view of foreign media and international election observers out in force on the islands.

"We have freedom today at last after 40 years," said Mohamed Ahmed, 21, holding a poster of CUF leader Seif Sharif Hamad. "We have won. Goodbye CCM!" sang others.

Opposition presidential candidate Hamad, whose party wants privatisation and democratic reforms, said the results his party gave out were based on results sheets seen by his agents.

But government spokesman Vuai Ali Vuai said that was premature. "Our friends want to make chaos by telling the world results before they are counted … We have great hope we will be the winner," he told Reuters.

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