Updated

Many of the millions of Zimbabweans living abroad won't return home for key general elections next week, sceptical of a fair outcome after years of election violence.

President Robert Mugabe has vowed to extend his 33-year-rule and beat bitter rival Prime Minister Morgan Tsvangirai at the polls on July 31.

The vote will choose a successor to the pair's tense unity government, but those who fled the nation's downward spiral into political and economic crisis doubt the prospect of a new beginning.

"This is a make or break election for Zimbabwe, but as important as it is, in my opinion, I can't help but feel that it's a futile exercise," said Justice Chikodzera, an immigrant in South Africa.

An unemployed teacher, Chikodzera counts among around two million Zimbabwean immigrants living in their neighbouring country.

Here some of Zimbabwe's brightest young minds work for a pittance as restaurant waiters or car guards, drawn by South Africa's economic clout after fleeing election violence in their nation.

Zimbabwean laws do not allow people residing outside the country to vote, so the masses of eligible voters who live abroad have to travel home to draw their cross.

Except many won't.

Chikodzera said he was discouraged by his country's history of "vote-rigging to suit certain parties".

Despite closely following the political events back home, he won't return to vote, but still urged his countrymen to choose wisely.

"This time we need to prove to the world that we can determine our future," he said.

Tsvangirai won the first round of voting in previous polls in 2008, but pulled out of run-off elections after around 200 opposition activists were killed in violent clashes.

Mugabe and Tsvangirai were forced to share power a year later, but their unity government has failed to reform the security forces and media despite a new constitution approved in a referendum in March this year.

Emigrants doubt that polls this time round will be fair, said Abius Makadho, a representative of Tsvangirai's Movement for Democratic Change (MDC) in South Africa.

People feared being singled out for attacks by supporters of Mugabe's ZANU-PF party, said Makadho.

"So far nothing suggests that the vote will be fair," he said from Diepsloot, a densely-populated slum north of Johannesburg.

He echoed concerns that ZANU-PF may have tampered with the voters' roll to stuff ballot boxes later.

"Many people have told us that they aren't registered. Others registered but their names don't appear on the voters roll," he said.

"So they have lost interest."

Rights groups have raised the alarm because the register of voters still counts names of people who have already died.

There are increasing fears that supporters of Mugabe, 89, who eyes another decade in power, won't accept defeat.

But some Zimbabweans will still make the journey to choose new leaders.

One of them is Nyasha Nzvimbo, a law graduate who works as an attendant at a service station in South Africa.

"This election should serve as a lesson that political violence won't take us forward," he said determined.

"People yearn for returning home. They want to return to a free and flourishing Zimbabwe, led by credible leaders," he said.

Mugabe proclaimed the election date earlier than planned, leaving the candidates only a month to campaign and organisers scrambling to prepare for elections the rest of the world will watch with a hawk's eye.

The candidates have criss-crossed the country courting votes in the past month, trying to fit into weeks campaigns that usually take months.

But thousands of security forces missed out on chaotic voting in special elections earlier in July, sounding an ominous note for the upcoming polls.

Time constraints made organising the vote "tough", leaders from regional mediator the Southern African Development Community acknowledged after an ad hoc-meeting on Saturday.

A Zimbabwean academic based in Johannesburg believes the polls were too rushed to allow people decide on their preferred candidate.

"The time wasn't enough to allow parties time to state their position, and for the voters to make up their minds," said Tawana Kupe from the University of the Witwatersrand.

"The campaign period is not only about the politicians," he said.