Uganda's veteran leader Yoweri Museveni was expected to extend his power into a fourth decade as people voted Thursday in presidential and parliamentary polls amid long delays.

Voting was due to begin at 07:00 am (0400 GMT) but the process was stalled for up to four hours in numerous polling stations where ballot boxes and papers did not arrive on time.

The long delays occurred especially in the capital Kampala, where the opposition usually gains many votes.

Election commission spokesman Jotham Taremwa said, "there was a bit of a delay at some polling stations because of logistical problems."

At one Kampala polling centre, hundreds of frustrated voters shouted and gesticulated at election officials. "They are denying us our constitutional right," said Elias Bukenya, a 27-year old teacher who suspected foul play.

Social media, including Facebook and Twitter, were largely inaccessible on voting day although Internet-savvy Ugandans dodged the apparent shutdown using virtual private networks.

Government regulator, the Uganda Communications Commission, said the attempted shutdown was for "security reasons" without giving details.

Museveni is widely predicted to win a fifth term, with the 71-year-old former rebel fighter who seized power in 1986 entering his fourth decade in power.

The strongest among seven challengers is Kizza Besigye, 59, who is making his fourth run at the presidency and ended his campaign claiming the election would be neither free nor fair.

At polling stations where voting got underway more or less on time, experienced voters turned up anticipating a long wait in the hot sun.

At Nakulabye in the capital Fred Musoke, 34, said, "I came ready -- I packed tea and pancakes to wait until I vote."

Motorbike taxi driver Etima Karim, 35, said he would vote for Besigye.

"He has to change things like health, hospitals and roads," Karim said, as he waited for a polling station to open in Kampala.

Over 15 million Ugandans are registered to vote, casting ballots in more than 28,000 polling stations for both a president and members of parliament, with 290 seats being contested by candidates from 29 political parties.

Over 150,000 police, soldiers and other security forces have been deployed to ensure tight security, according to election officials.

Polls are due to close at 04:00 pm (1300 GMT) with counting to begin soon after. Initial results are expected as early as Saturday afternoon with the leading candidate requiring more than 50 percent of votes cast to avoid a second round run-off.

Elections in 2006 and 2011 were marred by violent, and occasionally deadly, street protests and the liberal use of tear gas by heavy-handed police. However, apart from an outbreak of violent protests in which one person died on Monday, campaigning was relatively peaceful this time.

Voter turnout has followed a downward trajectory in recent elections with nearly three-quarters of eligible voters casting a ballot in 1996, during the country's first-ever competitive election, but only three-fifths bothering to turn out in 2011.

Museveni's share of those votes has also declined but most 2016 polls give him more than the 50 percent needed to avoid a run-off. He won his last five-year term in 2011 with 68 percent.

The other main challenger, Amama Mbabazi, a 67-year old former prime minister and ruling party stalwart, accused the Museveni's National Resistance Movement of planning to stuff ballot boxes even before voting began.