Thousands of protesters filled Cairo's Tahrir Square overnight as Egypt's rival presidential candidates, an Islamist and former general, accused each of trying to steal an election whose result is still not known five days after polling ended.

Another two days of uncertainty and name calling seem likely over the weekend which begins on Friday, though there was no immediate violence.

With confidence ebbing away in a process Egyptians hoped would secure the democracy they thought they had won with blood spilt on the square over a year ago, those camping out overnight demanded military rulers reverse new orders that entrench the generals' power and called on the election commission to declare the Muslim Brotherhood's Mohamed Morsy president.

Across town, in a luxury international hotel, former general Ahmed Shafik, who was Hosni Mubarak's prime minister when the army forced out the dictator to appease the Tahrir protesters, challenged Morsy's self-proclaimed victory and said he was sure he had won, despite Islamist pressure on officials.

At a televised address to whooping and cheering supporters, Shafik said: "These protests in the squares, the campaigns of terror and the media manipulation are all attempts to force the election committee to announce a particular result."

Speaking in person rather than through spokesmen as he has through the week, he added: "I am fully confident that I will be the legitimate winner." He called for calm and unity, saying he would invite opponents to join his administration.

In a country where ballot fraud was the norm during 60 years of military rule, trust is low, not least among Brotherhood officials who note that the electoral commission itself is made up of judges appointed under Mubarak. A parliamentary vote in November 2010 that handed Mubarak's party 90 percent of the seats was one of the triggers for the fury that overthrew him.

Military rule

The military council, which has promised to hand over to civilians by July 1, dissolved a new, Islamist-led parliament on the eve of the presidential run-off and then issued a decree as polls closed on Sunday setting strict limits on the powers of whoever would be elected president.

The Islamists say they fear the delay in announcing the vote result is part of a plot to deny them the victory that Morsy declared within hours of the polls closing.

The Brotherhood has released chunky volumes of what it says are official documents from polling stations allowing it to conclude Morsy won by four percentage points. Shafik's camp says the Brotherhood is trying to intimidate officials to secure victory, or set the stage for protests if it loses.

Sources on the commission, and in the military, said earlier in the week that preliminary data favoured Morsy - but officials are now bogged down in days of hearing complaints and appeals. Friday and Saturday are the weekend and officials have suggested that a result on Sunday is now likely, though not certain.

"We are taking our time to review the appeals to investigate them properly but, God willing, the results will be announced by Sunday at latest, if not before that," Judge Maher el-Beheiry, a member of the election committee, said.

Tahrir Square

Among thousands who packed Tahrir after dark, waving Egyptian flags and singing in what has become a familiar ritual over the past year, Ahmed Youssef said he and his friends, Islamists from a province north of Cairo, would camp out overnight to join a major rally after weekly prayers on Friday.

"We thought the army would stand by the revolution, and were surprised when it didn't," said the bearded electrical engineer, 24, who supports a hardline Salafist Islamist group.

"We will stay here until the military council hands over power," he added, voicing a widely-shared sense of betrayal by generals who promised to rule only until elections.

Ehab al-Bahrawy, 29, a preacher and chicken farmer from the distant suburbs of Cairo said: "I am staying until Dr. Morsy takes all his rightful powers. This is an open-ended sit-in."

The Brotherhood have called for permanent vigils in town squares across the country.

Muslim Brotherhood spokesman Mahmoud Ghozlan said the delay "generates concern, no doubt", expressing fear that the authorities were getting ready to announce Shafik the winner.

"The doubt extends to this possibility," he told Reuters.

Egyptian media have described a nation on edge.

"Egypt on the verge of exploding," Al-Watan daily wrote in a front-page headline, highlighting worries about how supporters of rival camps will respond if their candidate loses. "Security alert before the presidential result," wrote Al-Masry Al-Youm.

"The interest of the nation goes before narrow interests," said reformist politician Mohamed ElBaradei, a former UN diplomat and Nobel peace laureate on Twitter. "What is required immediately is a mediation committee to find a political and legal exit from the crisis. Egypt is on the verge of explosion."

Adding to unease, Mubarak is himself back in the news, being transferred to a military hospital from the prison where he began a life sentence this month. Security sources have said the 84-year-old was slipping in and out of a coma but "stabilising". Many Egyptians suspect the generals are exaggerating his illness to get their old comrade out of jail.

Mohamed Abdel Razek, a Mubarak defence lawyer, said the former president had a stroke on Wednesday after he had a fall during an accompanied visit to a bathroom at Tora prison.