CAIRO – Egypt braced for mass rallies on Sunday with President Mohamed Morsi's opponents determined to oust him and his Islamist supporters vowing to defend his legitimacy to the end, stoking fears of a violent first anniversary of his taking office.

Thousands of jubilant protesters gathered in Cairo's Tahrir Square ahead of the scheduled marches, waving Egyptian flags as patriotic songs boomed from large speakers.

"The people want the ouster of the regime," the protesters chanted, the signature slogan of the 2011 revolt that ousted Hosni Mubarak and brought Morsi to power.

Some protesters held up red cards, others wore black headbands with "Leave, Morsi!" written on them.

"This is the second revolution and Tahrir is the symbol of the revolution," said carpenter Ibrahim Hammouda, who travelled from the northern city of Damietta to join the protest.

Marchers were scheduled to set off at 5 pm (1500 GMT) for the Ittihadiya presidential palace, close to a neighbourhood where thousands of Morsi supporters vowed to pursue a counter-demonstration in defence of the president.

Anti-Morsi demonstrations were also expected in provincial cities.

Police and troops have deployed to protect key buildings around the country, security officials said. The health ministry said hospitals have been placed on high alert.

A senior security official said the Suez Canal, the vital waterway that connects the Mediterranean with the Red Sea, has been placed under "maximum security."

The streets of Cairo were unusually quiet for the first day of the working week in Egypt, with banks and most offices closed.

The grassroots movement Tamarod – Arabic for rebellion – is behind a campaign that claims to have collected millions of signatures to a petition demanding Morsi's resignation and new elections.

Posters calling on people to join the protests against his rule have sprung up around Cairo, plastered on walls and stuck on car windows, along with "June 30" graffiti.

The week leading up to the showdown has already seen eight people killed, including an American, and scores more injured as protesters from both sides took to the streets.

Morsi, previously a senior Muslim Brotherhood leader, is Egypt's first freely elected president, catapulted to power by the 2011 uprising that ended three decades of authoritarian rule by Mubarak.

His opponents accuse him of betraying the revolution by concentrating power in Islamist hands and of sending the economy into free fall.

But his supporters say that many of the challenges he faces he inherited from a corrupt regime, and that he should be allowed to serve out his term which ends in 2016.

Any attempt to remove him from office, they say, is a coup against democracy.

Leading opposition figure, Nobel peace laureate Mohamed ElBaradei, urged the president "to listen to the people" and step aside.

The fervent displays of emotion from both camps highlight the deep divisions in the Arab world's most populous country.

The army, which led a tumultuous transition after the revolt that ousted Mubarak, has warned it will intervene if there is major unrest.

Since taking office, Morsi has battled with the judiciary, the media and the police. The economy has taken a tumble, investment has dried up, inflation soared and the vital tourism industry has been battered.

Many Egyptians stocked up on food and withdrew cash in anticipation of Sunday's rallies. Adding to the tension, fuel shortages caused long queues outside petrol stations, bringing some parts of the capital to a standstill.

On Saturday, at least eight deputies resigned from the Islamist-dominated Shura Council, in a boost for Tamarod which says it now has 22 million signatures to its petition demanding a snap election and Morsi's departure.

The figure, which compares with the 13.2 million votes to 12.3 million by which Morsi won election last year, cannot be verified.

Morsi's camp is determined to defend his legitimacy.

"We will not allow a coup against the president," senior Brotherhood leader Mohamed al-Beltagui told a Cairo rally.

Demonstrator Kamal Ahmed Kamel echoed his comments. "It's not just about Morsi, it's about legitimacy and the state. We can't go backwards," he said.

Others called on the opposition to invest their energy in the political process.

Morsi's opponents reject the idea that removing him is a "coup", saying calls for his resignation are aimed at bringing the revolution back to its cornerstones of democracy, freedom and social justice.

In a televised speech on Wednesday, Morsi warned the polarisation threatened to "paralyse" Egypt as he tried to placate protesters with appeals for dialogue and promises of constitutional reform.

Speaking in South Africa, US President Barack Obama voiced concern at developments in Egypt and urged Morsi and his opponents to be more "constructive."

"Everybody has to denounce violence. We would like to see the opposition and President Morsi engage in a more constructive conversation about how to move their country forward."