Updated

Millions of Ugandans lined up to vote Friday in the east African nation's presidential ballot pitting the country's long-serving president against his former ally and personal physician, officials said.

Opposition threats of street protests and the looming start of oil production have raised the stakes in the vote — just the second multiparty election to be held in Uganda in 30 years.

President Yoweri Museveni, who is vague about his age and says he is 66 or 67, faces a record seven challengers.

A U.S. ally, Museveni predicts a "big win," and most analysts agree he is likely to claim a fourth term. He faces his stiffest competition from a former ally and personal physician, 54-year-old Kizza Besigye.

Most polling stations in Uganda opened on time Friday, said John Mary Odoy, the director of a local election observer group, the Democracy Monitoring Group.

About 14 million people are registered to vote for the presidential and parliamentary races being decided.

Odoy said, however, that delays have been experienced throughout the Ugandan capital, Kampala. He said materials were delivered late and there were reports of officials not having vehicles to transport the ballot boxes.

An Associated Press reporter saw long lines of voters at some polling stations in Kampala that opened 90 minutes late.

Voting was supposed to begin across the country at 7 a.m. (0400 GMT).

Paul Bukenya, a spokesman for the Electoral Commission of Uganda, downplayed the problems in Kampala.

"We have been waiting for hours, but they are so delayed," said voter Robert Mwanja, a 35-year-old shopkeeper. He was queuing at an open-air polling station at Nakasero market in central Kampala. "The officials are so confused. They don't know what they are doing."

Security has been heightened around Kampala and at the nation's nearly 24,000 polling stations.

Beyond potential election violence, police and embassies warned of possible terrorist attacks. Last July twin suicide bombings in Kampala claimed by the Somali militant group al-Shabab killed at least 76 people.

Police spokeswoman Judith Nabakooba said Thursday night the situation in the country had been generally calm with only isolated disturbances.

Museveni's main challenger, Besigye, already has called the election "fundamentally flawed," pointing to the incumbent's control of the electoral commission and the failure to give new voters identity cards as proof that the president will rig the vote.

Besigye, the candidate for the Inter-Party Cooperation coalition, lost to Museveni in 2001 and 2006, and failed to get the results overturned in court, despite proof of widespread intimidation.

This time around, he plans to release his own tally of results and has ruled out launching a court challenge. Instead he has threatened street protests and insists that 25 years after Museveni seized power as the head of a rebel group Uganda is ready for an Egypt-style popular revolt.

"I am voting for change. We need change," said Stephen Asiimwe, 40, a market vendor. "I am not a fool to let someone rule for 30 years."

Others hoped Museveni would win a fourth term.

"Let me give him one more chance and see what he can do," said Edward Bbaale, 40, a garbage collector.

Bbaale said that despite living conditions remaining stagnant, he supported Museveni for the peace and stability he has brought to the country.

"I pray to God that the one that loses the election accepts defeat peacefully," he said.