Egyptians will learn the winner of a divisive presidential election on Sunday after the results were delayed following victory claims by both candidates that have sparked tensions between the rival camps.

The electoral commission overseeing the contest between Muslim Brotherhood candidate Mohamed Morsi and former prime minister Ahmed Shafiq said it would announce the official winner at 3:00 pm (1300 GMT).

By Saturday evening, hundreds of Brotherhood supporters determined to occupy Cairo's iconic Tahrir Square until the election result was published, had been joined by others, swelling their numbers to the thousands.

"Morsi, Morsi, God is the Greatest," the protesters chanted in anticipation of a victory for their candidate.

Across the city, in the Nasr City neighbourhood, thousands of Shafiq supporters held up pictures of their candidate and of military ruler Field Marshal Hussein Tantawi, chanting "the people and the army are one."

"Down with the rule of the Supreme Guide," protesters shouted, referring to the head of the Muslim Brotherhood.

Both Morsi and Shafiq have claimed victory in the election for a successor to Hosni Mubarak with tensions deepening after the electoral commission delayed announcing the official outcome.

A huge security plan has been put in place in the capital to prevent unrest when the result is announced, an interior ministry official told AFP.

The delay in the announcement of the result of the June 16-17 run-off, initially scheduled for Thursday, has raised suspicions that the outcome of the election is being negotiated rather than counted.

As the Supreme Council of the Armed Forces (SCAF) and the Brotherhood clashed publicly over recent measures that consolidated the army's power, privately they have been talking behind the scenes, sources told AFP.

On Friday, the SCAF warned it would deal "with utmost firmness and strength" with any attempts to harm public interests.

The Brotherhood, for its part, warned against tampering with the election results, but said it had no intention of instigating violence.

It has rejected a constitutional declaration by the military that strips away any gains made by the Islamist group since the popular uprising which forced Mubarak to stand down in February last year.

The document dissolves the Islamist-led parliament and gives the army a broad say in government policy and control over the new constitution. It was adopted just days after a justice ministry decree granted the army powers of arrest.

Those changes mean that even if Mursi wins the election, the Brotherhood is left with no parliament, no say in the constitution and a powerless president.

"It's a problem which we are trying to resolve," one Brotherhood official said.

The election has polarised the nation, dividing those who fear a return to the old regime under Shafiq's leadership from others who want to keep religion out of politics and who fear the Brotherhood would stifle personal freedoms.

Shafiq ran on a strong law-and-order platform, pledging to restore security and stability. He is himself a retired general but as a Mubarak-era minister he is reviled by the activists who spearheaded the 2011 revolt.

Morsi is the Islamists' fallback representative after their deputy leader Khairat el-Shater was disqualified.

He has sought to allay the fears of secular groups and the sizeable Coptic Christian minority by promising a diverse and inclusive political system in Egypt.