Tanzania's outgoing President Jakaya Kikwete said Friday he was "happy" to be leaving his job after a decade in power, having stepped aside after serving his two-term limit.

Ruling party candidate John Magufuli won Tanzania's hotly contested presidential elections with over 58 per cent of votes, cementing the long-running Chama Cha Mapinduzi (CCM) party's firm grip on power, officials announced on Thursday.

His running mate Samia Suluhu Hassan will become Tanzania's first ever female vice president.

READ: Magufuli win gives Tanzania first female vice president

Kikwete, speaking at a ceremony to hand formal winning certificates to Tanzania's new leaders, said he was now going to his home village of Msogo, some 100 kilometres (60 miles) west of the economic capital Dar es Salaam.

He dismissed a question as to whether he would miss the trappings of office.

"Why should I be sad? You see I'm so happy, I played my part, now I have to move on, let a new team come and take the nation further," Kikwete said, calling Magufuli the "right person" for Tanzania.

"I was given the opportunity, and for 10 years I worked to the best of my ability to build our nation. Time has now come for me to leave the country peacefully to the next leader."

Kikwete's standing down comes amid a wider controversy in Africa over efforts by leaders to change constitutions in order to stay in office.
But Tanzania's vote was not without controversy.

The opposition has said the vote was rigged and has also claimed victory, while the semi-autonomous Zanzibar archipelago's decision to annul polls has also caused concern. The islands were reported to be calm on Friday, according to an AFP reporter.

Magufuli, a former chemistry teacher who celebrated his 56th birthday on Thursday as results were announced, ran on an anti-corruption platform, and secured a convincing victory over his closest rival, ex prime minister Edward Lowassa who won 40 per cent.

Lowassa, a former CCM stalwart turned opposition chief, rejected the official results and accused the election body of falsifying tallies.