Vote counting underway in Tanzania's tightest

The first results are due Monday, with the final results expected by Thursday.

The semi-autonomous island archipelago of Zanzibar is also voting for a president and local leaders. CUF said the attack on its supporters was meant to "intimidate the opposition".

Both Magufuli and Lowassa have drawn tens of thousands of people to lively rallies, vowing to curb frequent power outages, halt corruption and deliver economic growth that will deliver more jobs to the poor.

The National Electoral Commission disqualified four candidates- Mchungaji Mtikila, Godfrey Malisa, John Lafichipaka and Omari Sombi- after they failed to meet the minimum threshold to qualify for the presidential race.

Official results are not expected out until later this week.

"I have won by 52.87% against the incumbent president Dr Ali Mohamed Shein's 47.13%", Hamad said. "The commission therefore should not do anything against the decision of the people".

Among the frontrunners in the race to Tanzania's Presidential seat is former Prime Minister Edward Lowasa of Chadema, who decamped to the opposition following CCM's decision to opt for John Magufuli as its presidential nominee.

In the run-up to the polls, the opposition has accused CCM of using state institutions to rig elections and intimidate its supporters, something the party and the government deny.

Late on Sunday Chadema party, part of the opposition coalition led by Lowassa, said police raided its vote-tallying centre in Tanzania's commercial capital Dar es Salaam and arrested opposition officials.

British High Commissioner Dianna Melrose said she was generally impressed with the polls. High turnout was reported in several areas, and queues snaked around corners amid complaints of long delays.

"The local and regional authorities who we are going to elect will have a huge responsibility", President Juan Manuel Santos said, encouraging Colombians to vote. "However, the prospect of electoral violence looms heavy on the minds of many".

CCM's election coordinator Yusuf Makamba warned the opposition against making "inflammatory statements" adding that such comments "may spark unrest".

Lowassa and Kikwete met as students at the University of Dar es Salaam, brought together by their interest in politics. "Generally the election has been conducted in a manner that is credible but every party has expectations". While there's little difference in key policies between Lowassa and Magufuli, the ex-premier may benefit from discontent with the CCM as well as a wave of enthusiasm for his candidacy that's been stoked by social media. "There's clear popular enthusiasm for something different than the same old, same old CCM again", said J. Peter Pham, director of the Africa Center at the Atlantic Council, a think tank in Washington, D.C. "It's hard to run an anti-corruption campaign when he was forced to resign in 2008 under the shadow of financial impropriety".