Social media has been blocked and an opposition candidate briefly arrested as voters in Uganda went to the polls in the country's hotly contested election.

Incumbent President Yoweri Museveni has been in power for 30 years and is looking to extend his grip on power.

Interviewed on TV about the social media, Mr Museveni, 77, reportedly said the ban the election was to stop people "telling lies".

"Some people misuse those [social media] pathways." He said.

His main political rival Kizza Besigye was briefly detained by police, according to the Reuters news agency.

Another political rival of Museveni, Amama Mbabazi, tweeted about the social media blackout - which included the Whatsapp messenger service - and urged Ugandans to use a VPN (Virtual Private Network) to access the sites and applications.

Meanwhile, Reuters reports that Museveni took an early lead in the country's election, according to preliminary results from the Electoral Commission.

The commission said Museveni garnered 1.36 million votes out of a total 2.32 million votes counted from 6,448 polling stations out of a total 28,010 stations.

The tally gave Museveni 61.75% of the votes counted, followed by opposition leader Besigye with 33.47%.