A supporter of Tanzania's ruling Chama Cha Mapinduzi (CCM) presidential candidate John Pombe Magufuli cheers during a campaign rally at Jangwani grounds in Dar es Salaam, Oct. 23, 2015. Reuters/Sadi Said

DAR ES SALAAM (Reuters) - Tanzanians voted on Sunday in presidential and parliamentary polls in which the ruling party is expected to fend off rivals led by former prime minister Edward Lowassa, who has tapped into mounting anger over corruption and the slow pace of change.

In power for more than half a century, the ruling CCM party has faced growing pressure to speed up development of Tanzania's significant natural gas resources to spur economic growth and lower stubbornly high poverty rates.

Polls and analysts forecast a presidential victory for John Magufuli, a CCM candidate, but many expect the party's parliamentary majority to be whittled down after the opposition united behind a single candidate for the first time.

"I'm voting for Lowassa because his policies give Tanzanians hope. We've been tired for a very long time of the ruling party," Joram Murawa, a businessman, said before polls opened at 7 a.m. (0400 GMT). Voting was due to end at 1300 GMT.

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.

On the eve of the vote, Lowassa, who defected from CCM in July after the party spurned him as a possible leadership candidate, said he would only concede defeat if the vote was free and fair.

"If it's not, I won't concede," Lowassa told reporters after stepping off the podium at his final rally.

Any dispute over the election outcome could raise tensions in a nation which has been relatively stable since its independence in 1961.

Outgoing President Jakaya Kikwete, who will step down after serving two terms, has urged against violence in the lead-up to the polls. Some officials and analysts have voiced concerns about rising tensions in the archipelago of Zanzibar, where the opposition has accused the government of intimidation.

"Anyone who tries to cause trouble will be dealt with," Kikwete said at a CCM rally on Saturday.

Both Magufuli and Lowassa have drawn tens of thousands of people to lively rallies, vowing to curb frequent power outages and ensure future economic growth reaches the poor.

They have also pledged to tackle rampant corruption, pave roads and improve crumbling infrastructure that hinders businesses and weighs on everyday life.

At a final rally on Saturday, Magufuli said he would focus on creating jobs and ensuring faster development of Tanzania's natural gas discoveries.

Tanzania's ambitious plans to build a multi-billion-dollar liquefied natural gas (LNG) plant appear to have stalled, a major concern in a nation which is counting on its gas resources to turbo-charge its development.

The new president will also need to do more to encourage foreign investment and shake off Tanzania's reputation for letting bureaucracy hamper development.