Long queues were reported for parliamentary and presidential elections in Ghana, seen as a model for democracy in Africa. As polls opened, state-owned radio said there were queues in all regions of the country.

President John Mahama, 54, is expected to face a strong challenge from Nana Akufo-Addo, 68.

Mr Mahama, from the National Democratic Congress, took over as president after John Atta Mills died suddenly in July.

The 2008 election was decided by just 30,000 votes in the run-off.

After gaining the most votes in the first round, Mr Akufo-Addo, from the then governing New Patriotic Party (NPP), was praised for peacefully accepting his defeat.

'Ready to go'

Ghana's electoral commission chief told the BBC everything was ready for Friday's polls. Kwadwo Afari-Gyan said the new biometric voter identification system had worked smoothly during extensive tests.

Ghana has held two peaceful transfers of power since military rule ended in 1992.

"We are ready to go," Mr Afari-Gyan told the BBC's Focus on Africa programme.

He said that all the election material had already been delivered to districts and constituencies around the country.

He said the new biometric system had been tested over two months and again earlier this week, when security personnel voted, but added that if there were any problems, voting would be extended until Saturday.

Some 14 million people have registered to vote in 26,000 polling stations nationwide.

"If everything is normal and goes smoothly, we give ourselves 72 hours [to announce the result]," he said.

There are eight presidential candidates overall.

The BBC's David Amanor in the capital, Accra, says there is an air of excitement in the country after the end of weeks of frantic campaigns.

As well as being praised for its democracy, Ghana also has one of Africa's fastest growing economies, thanks to its recently tapped oil reserves.

Both Mr Mahama and Mr Akufo-Addo have promised to accept the result, but 5,000 soldiers have been put on standby just in case.

A run-off will be held on 28 December if no candidate wins more than 50% of Friday's vote.

There are six other presidential contenders and hundreds of candidates for the 275 parliamentary seats.