By Christopher Johnson
FREETOWN (Reuters) - Gunfire broke out in Sierra Leone's second biggest town, Bo, on Friday as supporters of rival political parties clashed in the streets, sources said.
The fighting erupted after a leading opposition figure and presidential hopeful, Maada Bio, was struck on the head by a stone during a campaign trip to the town.
"Suddenly we got attacked by stone-throwing thugs from the (ruling) APC party," said Abass Bundu, an advisor to Bio traveling with his delegation. "There have been lots of gunshots by the police," he said.
A police official and two residents in Bo reached by telephone said the fighting was heavy on Friday afternoon and that buildings had been set on fire.
It was unclear if anyone was killed or hurt. A government official was not immediately available to comment.
The clashes reflect rising tensions in the West African state, still scarred by a 1991-2002 civil war, ahead of elections set for 2012.
Bio, who briefly ran the country in 1996 as the head of a military junta, is the Sierra Leone People's Party's candidate for next year's poll.
He will run against incumbent President Ernest Bai Koroma, who's ruling APC party has accused Bio of human rights violations during the civil war, charges he denies.
Next year's elections -- likely to take place in the autumn -- will fall 10 years after the end of the civil war and will be seen as a bellwether of the country's return to stability.
One of the world's poorest countries, Sierra Leone is hoping the elections will pave the way for new investment in its mining and energy sectors.
(Reporting by Christo Johnson and Simon Akam; Writing by Richard Valdmanis; Editing by Jon Hemming)