Egypt's election authority is preparing to announce the result of last weekend's presidential run-off vote.
The panel of judges has begun announcing its decisions on the hundreds of complaints by the campaigns of Mohammed Mursi and Ahmed Shafiq.
Security is tight, with tanks deployed around the commission's headquarters.
Both Mr Mursi, a leader of the Muslim Brotherhood, and Mr Shafiq, a former prime minister, have claimed victory and vowed to form unity governments.
Thousands of Mursi supporters have gathered in Tahrir Square to hear the result and are urging the ruling military council to respect the will of the people. Some are chanting "revolution, revolution until victory".
A pro-Shafiq rally is being held in the northern district of Nasser City.
Correspondents say the atmosphere at both gatherings has been peaceful, but tense.
Many people are still apprehensive about the intentions of the ruling generals, who gave themselves sweeping new powers last week after the Supreme Constitutional Court ruled that the Islamist-dominated parliament should be dissolved.
Shops are closing early and people are hurrying to their homes to watch the decisive news conference at the Higher Presidential Election Commission headquarters in Nasser City.
Government employees were also advised to leave early, in another signal of the security precautions being taken, the BBC Arabic's Dina Demrdash in Cairo says.
On Friday, the Supreme Council of Armed Forces (Scaf) called on supporters of both candidates to accept the result when it came.
Results from last weekend's run-off were originally due out on Thursday.
Muslim Brotherhood supporters are maintaining a vigil in the capital's Tahrir Square, where on Friday tens of thousands of protesters gathered to denounce a series of decrees and appointments by the Scaf designed to reduce or constrain the power of the president, and entrench the power of the military.
Demonstrators held a noon prayer meeting in the square, which was the birthplace of the uprising that ousted Hosni Mubarak some 17 months ago.
On 13 June, the military-controlled government gave soldiers the right to arrest civilians for trial in military courts until the ratification of a new constitution.
Four days later, just as the polls were closing in the presidential run-off, the generals issued an interim constitutional declaration that granted them all legislative powers and reinforced their role in the drafting of a permanent constitution. The document also exempted the military from civilian oversight.
Then on Monday, the head of the Scaf, Field Marshal Mohammed Hussein Tantawi, announced the re-establishment of a National Defence Council, putting the generals in charge of Egypt's national security policy.
Islamists, liberals and secularists said the moves amounted to a coup.
"The military must leave its political role and go back to its basic role which is protecting the country, not continuing to ruin the country and people's affairs - this will not be accepted by the Egyptian people," Abdel Nasser Hijab, a demonstrator in Tahrir Square, told the Associated Press.
The BBC's Jon Leyne in Cairo says there are fears that in the current atmosphere, the announcement of the presidential election results might only make matters worse.
On Tuesday, the Brotherhood's Freedom and Justice Party announced that Mr Mursi, its chairman, had won with 51.74% of the vote, citing official figures from the HPEC.
Mr Mursi has also secured the support of several leading liberal figures and youth activists in Egypt, including Wael Ghonim, who played a key role in the uprising that forced Hosni Mubarak to step down in February 2011.
Mr Shafiq came second to Mr Mursi in last month's first round, in which turnout among the 52 million eligible voters was only 46%.
But the former air force commander, who served briefly as former President Mubarak's last prime minister, said on Thursday at his first public appearance since the run-off that he was confident of victory.