KAMPALA (REUTERS) - Ugandans started casting their votes on Thursday (Feb 18) to decide whether to give incumbent President Yoweri Museveni, in power for three decades, another term in office.

Voting at most polling stations in the capital, Kampala, was yet to start 90 minutes after the official opening of polling at 7 am local time (12 pm Singapore), leading to concerns among some voters.

"If the voting time is reduced like this, there will be many people who will not be able to vote," said Dickson Mamber, a 34-year-old history teacher, who had been waiting in line for two hours at Muyembe polling station in Kampala.

Voting at the station still had not started by 8.45 local time (1.45 pm Singapore). All sides contesting the election accuse each other of stoking tensions and assembling vigilante groups, and the leading opposition candidates have predicted vote rigging.

Museveni, 71, has pleased Western allies by sending in peacekeeping troops to hotspots such as Somalia. He faces two main challengers - longtime opposition leader Kizza Besigye, who has run unsuccessfully in three previous elections, and former prime minister Amama Mbabazi, who until recently was a close ally.

Besigye told Reuters on the eve of the vote Museveni was "not going to go peacefully" and said his supporters may stage street protests to dispute the election outcome. Museveni meanwhile warned opponents to expect a tough response from security services if violence erupts.

The United States last week supported calls for a peaceful, transparent and credible vote.

Museveni, who came to power in 1986 after waging a five-year guerrilla war, is hailed by many Ugandans as providing decades of relative peace and economic stability. His rivals, however, are drawing strength from a clamour for fresh leadership. Uganda is an overwhelmingly youthful country, and all the candidates have sought to stir the enthusiasm of younger voters.

Museveni's rallies featured performances by leading pop stars, while Besigye and Mbabazi have centred their campaigns on pledges to boost employment and tackle corruption, issues that young voters emphasise.

On the streets of Kampala, most young voters identified themselves as Besigye supporters. Joel Nyonyintono, a 26-year-old entrepreneur, said he was ashamed of the condition of Uganda's roads and hospitals and craved an innovative leader.

"We are so far behind. We need to open our eyes and move into the 'now' tense," Nyonyintono said as he sat near a church in Kampala.

Other voters say the idea of "change" makes them nervous.

Nanteza Beatrice, 56, a fruit vendor in a Kampala market, said she believed Uganda was not ready for a post-Museveni era.

"We have had peace for a long time and these young people are taking it for granted because they don't know how it was before him," she said.

Voting is scheduled to last for nine hours, ending at 4 p.m. (9 pm Singapore)