CAIRO: Egyptians head to the polls on Saturday to choose Hosni Mubarak's successor in a divisive runoff whose outcome will chart dramatically different paths for the Arab world's most populous nation.

The election pits ex-prime minister Ahmed Shafiq, who is running on a tough law-and-order platform, against the Muslim Brotherhood's Mohammed Mursi, whose movement has vowed to uphold the goals of the uprising that propelled it to the forefront of Egyptian politics.

Mursi came ahead with 24.7 per cent, against Shafiq's 23.6 per cent, in the first round of voting in May, which saw 13 candidates compete for the top job.

The race has polarised the nation between those who fear a return to the old regime under Shafiq's leadership and those wanting to keep religion out of politics and who accuse the Muslim Brotherhood -- which already dominates parliament -- of monopolising power since last year's revolt.

“It's the worst possible scenario,” said Hassan Nafea, professor of political science at Cairo University.

“If Shafiq is elected, this means the revolution has been aborted. If it's Mursi, the country will be run according to the Muslim Brotherhood programme, which most Egyptians reject,” he told AFP.

The difficult choice has garnered support for the boycott movement, largely ignored in the first round of voting.

Now high-profile activists and celebrities are calling on the 50 million registered voters to abstain or to void their ballots, highlighting the fact that the very same judiciary that issued the controversial Mubarak verdicts will oversee the election.

Mubarak and his interior minister Habib al-Adly were sentenced to life in prison on June 2 for failing to prevent the deaths, but six security commanders were acquitted over the killings of demonstrators during last year's uprising that left around 850 people dead.

The ruling sparked outrage, with protesters who took to the streets furious that no one had been found directly guilty of killing the protesters.

In the final days of campaigning, former air force chief Shafiq accused the Muslim Brotherhood of violence during last year's uprising and of arson attacks against his campaign headquarters.

He said a victory for the Islamic fundamentalists would bring Egypt “back to the dark ages”. For his part, Mursi has pledged that Egypt under his leadership would be inclusive, as he courts secular and Christian voters.

He told reporters on Wednesday that his presidential institution would “include all forces, presidential candidates, women, Salafis and our Coptic brothers.” He pledged to end “discrimination against any Egyptian based on religion, ethnicity or gender.” But the race is threatened by a hearing in which the Supreme Constitutional Court will examine the constitutionality of the political isolation law which bars senior Mubarak era officials from running for public office.

The legislation, if approved, could bar Shafiq from continuing as a candidate, nullifying his votes in the first round and requiring a new election, judicial sources said.

However, it is not clear whether the court will rule in advance of Saturday and Sunday's election.

The next president will inherit a struggling economy, deteriorating security and the challenge of uniting a nation divided by the uprising and its sometimes deadly aftermath, but his powers are yet to be defined by a new constitution.

The election caps a rollercoaster transition, marked by political upheaval and bloodshed, but which also witnessed democratic parliamentary elections that saw fundamentalist groups score a crushing victory.

The Supreme Council of the Armed Forces (SCAF) has vowed to hand power to civilian rule by the end of June, after a president is elected, but many fear its retreat will be just an illusion.

The army, with its vast and opaque economic power, wants to keep its budget a secret by remaining exempt from parliamentary scrutiny, maintain control of military-related legislation and secure immunity from prosecution.