With victory for the 84-year-old Mugabe a foregone conclusion, his longtime rival Morgan Tsvangirai said the ballot was worthless while the US and European Union dismissed the process as a sham.

Mr Tsvangirai, leader of the Movement for Democratic Change (MDC), won the first round 13 weeks ago with 47.9 per cent of the votes to Mr Mugabe's 43.2 per cent.

The MDC said Mr Mugabe has since tilted the election in his favour through a campaign of systematic violence and intimidation and Mr Tsvangirai pulled out of the contest last weekend.

Despite state media predictions of a 'massive' turnout, voting in Harare got off to a slow start although reports from rural areas suggested polling stations were busier there.

Mr Mugabe and his family voted in the Harare suburb of Highfields. Beaming at reporters after casting his ballot, he said: 'I feel very fit and very optimistic.'

Amid allegations that people were being intimidated to vote for Mr Mugabe, Mr Tsvangirai said there was no point in acts of defiance.

'Today's results will be meaningless because they do not reflect the will of the people of Zimbabwe,' he wrote in a letter to supporters.

'If possible, we ask you not to vote today. But if you must vote for Mr Mugabe because of threats to your life, then do so. If forced to cast your ballot for Mr Mugabe to avoid personal harm, then again I say do so.'

In some areas, there were allegations that officials were inspecting ballot papers before they were placed in boxes.

Polling was due to end at 1700 GMT (1am today, Singapore time).

The simultaneous March 29 presidential and legislative election saw Mr Mugabe's Zanu-PF lose control of Parliament for the first time since independence from Britain in 1980, although the outcome is being challenged in the courts.

Mr Tsvangirai's name still appeared on the run-off ballot papers after the electoral commission said it was too late for him to withdraw.

Commission spokesman Utloile Silaigwana said polling was proceeding 'with no major problems'.

Mr Mugabe said at his final campaign rally on Thursday that he wants to continue as President after ruling uninterrupted since independence. While he would be willing to talk to the opposition, negotiations would begin only after he had won a sixth term.

Foreign ministers from the Group of Eight industrialised powers said yesterday that they would not accept Zimbabwe's government as legitimate if it 'does not reflect the will' of the people, and deplored the 'systematic violence, obstruction and intimidation'.

Zimbabwe was also to be discussed by African Union foreign ministers preparing for a summit in Egypt next week.

'I don't think we are going to accept the result but we are still discussing,' one minister said.

Viewed in the first years after independence as a post-colonial success story, Zimbabwe has seen its economy collapse since thousands of white-owned farms were expropriated by the state at the turn of the decade.

The one-time regional breadbasket now experiences shortages of the most basic foods while inflation - officially at 165,000 per cent but in reality many times higher - is the highest in the world.

AGENCE FRANCE-PRESSE, REUTERS