Crowds had thronged the square from early in the day ahead of the president-elect's appearance on the eve of his official swearing-in.

Morsy, who won a run-off election earlier this month, was received with applause by the tens of thousands of people gathered in the birthplace of the revolt that overthrew his predecessor Hosni Mubarak last year.

He promised a "civilian state" and praised "the square of the revolution, the square of freedom," in what he called an address to "the free world, Arabs, Muslims... the Muslims of Egypt, Christians of Egypt."

Morsy symbolically swore himself in before the crowd, saying: "I swear to preserve the republican system... and to preserve the independence" of Egypt.

Before his triumphant arrival, chants against the ruling military which took over on Mubarak's overthrow rang out from among the crowd as people gathered from mid-morning under a searing sun.

In his speech Morsy, whose election has raised concerns among Egypt's sizeable Coptic Christian community, served the United States with advance warning that his politics will be markedly different from those of his ousted predecessor.

He told the Tahrir crowd he would work to secure freedom for Omar Abdul Rahman, a blind Egyptian cleric jailed for life over the 1993 World Trade Centre bombing.

"I will do everything in my power to secure freedom for... detainees, including Sheikh Omar Abdul Rahman," Morsy said in his address to the throng packing the hub of the 2011 revolution.

Abdul Rahman was convicted in 1995 for his role in the World Trade Centre bombing, plotting to bomb other New York targets including the UN, and a plan to assassinate Mubarak.

After taking the oath, Morsy will have to contend with the Supreme Council of the Armed Forces, headed by Mubarak's long-time defence minister Field Marshal Hussein Tantawi, that will retain broad powers after it formally transfers power.

The liberal Wafd newspaper reported that Tantawi will remain defence minister in the new government.

"Down with the power of the military," demonstrators chanted. "Field marshal, tell us the truth – is Morsy your president or not?"

Their slogans dented hopes expressed in an editorial in the flagship state-owned daily Al-Ahram that announcement of the details of Morsy's swearing-in would end speculation about the military's real intentions.

"The swearing-in should dispel once and for all the doubts raised by those who have used every means to question the military's readiness to hand over power," it said.

Differences over power transfer

The Muslim Brotherhood, from which Morsi resigned after winning the presidency, had called for a huge demonstration in Tahrir, under the slogan "Day of the transfer of power."

The presidency announced late on Thursday that Morsi would be sworn in Saturday before the Constitutional Court, after differences with the army over the transfer of power to the nation's first civilian president.

Morsy "will go at 9am GMT Saturday to the Constitutional Court to take the oath before the Court's general assembly", said a statement released by state news agency MENA.

Traditionally the president takes the oath in parliament, but Egypt's top court has ordered the disbanding of the Islamist-dominated legislature.

The military subsequently assumed legislative powers and also formed a powerful national security council headed by the president but dominated by generals.

By agreeing to be sworn in by the Constitutional Court, Morsy is effectively acknowledging the court's decision to dissolve parliament.

The SCAF also reserves the right to appoint a new constituent assembly should the one elected by parliament be disbanded by a court decision expected on September 1, even though  the Brotherhood insists that only parliament can appoint the assembly.

Media reports said Morsy was consulting a cross-section of Egyptian society before appointing a premier and a cabinet mostly made up of technocrats.

In a meeting with Egyptian newspaper editors reported by most dailies on Friday, Morsy pledged there would be "no Islamisation of state institutions" during his presidency.

Morsy has already met the SCAF chief, as well as a delegation from the Sunni body Al-Azhar, and another representing Egypt's Coptic church.

Amnesty International on Friday urged Morsi to break the cycle of abuse under Mubarak and put Egypt on the path to the rule of law and respect for human rights.

"Egyptians have heard many promises that their demands would be listened to and that things would change, but so far their hopes have largely been frustrated," said Salil Shetty, Amnesty's secretary general.

Ahead of his speech, Morsy attended the main weekly Muslim prayers at Al-Azhar, Sunni Islam's highest seat of learning. Its imam – religious endowments minister in the outgoing government – called in his sermon for an inclusive Egypt.

"This must be the homeland of all its citizens with equality between individuals in a true democracy in which all can express themselves while respecting morality," Mohammed Abdel Fadil al-Qawsi said.

The Brotherhood and Al-Azhar, whose imams are named by the Egyptian government, had strained relations under Mubarak, and Qawsi called on Morsy to maintain the institution's privileged position under his presidency.