CAIRO: Thousands of opponents and supporters of Egypt's president began massing in city squares in competing rallies Sunday, gearing up for a day of massive nationwide protests that many fear could turn deadly as the opposition seeks to push out Mohammed Morsi.

VIDEO: Egypt set for day of protests

Waving Egyptian flags, crowds descended on Tahrir Square in the heart of Cairo, one of multiple sites in the capital and around the country where they plan rallies. Chants of “erhal!” or “leave!,” rang out in the square, birthplace of the 2011 uprising that toppled autocrat Hosni Mubarak.

On the other side of Cairo, thousands of the Islamist leader's backers gathered not far from the presidential palace in a show of support. Some wore homemade body armor and construction hats and carried shields and clubs – precautions, they said, against possible violence.

There is a sense among opponents and supporters of Morsi that Sunday's rally is a make-or-break day, hiking worries that the two camps will come to blows despite vows by each to remain peaceful. Already at least seven people, including an American, have been killed in clashes the past week, mainly in Nile Delta cities and the coastal city of Alexandria.

The demonstrations on Sunday, the anniversary of Morsi's inauguration as Egypt's first freely elected leader, are the culmination of growing polarization since he took office.

In one camp are the president and his Islamist allies, including the Muslim Brotherhood and more hard-line groups. They have vowed to defend Morsi, saying street demonstrations cannot be allowed to remove a freely elected leader.

The other is an array of secular and liberal Egyptians as well as moderate Muslims and Christians – and what the opposition says is a broad sector of the general public that has turned against the Islamists. They say the Islamists have overstepped their election mandate, accusing them of trying to monopolize power and woefully mismanaging the country.

The opposition believes that with sheer numbers in the street, it can pressure Morsi to step down – perhaps with the added weight of the powerful military if it signals the president should go.

“Today, the people will triumph over fascism,” prominent pro-democracy campaigner and bestselling novelist Alaa al-Aswany wrote on his Twitter account.

Underlining the potential for deadly violence, a flurry of police reports on Sunday spoke of the seizure of firearms, explosives and even artillery shells in various locations of the country, including Alexandria and the outskirts of Cairo.

In an interview published Sunday in The Guardian, Morsi – who has three years left in his term – said he had no plans to meet the protesters' demand for an early presidential election.

“If we changed someone in office who (was elected) according to constitutional legitimacy _ well, there will (be) people or opponents opposing the new president too, and a week or a month later, they will ask him to step down,” Morsi told the British daily.

“There is no room for any talk against this constitutional legitimacy,” he said.

As the crowds swelled in Tahrir, traffic in the capital's normally clogged streets was light at midday as many residents chose to stay home for fear of violence or a wave of crime similar to the one that swept Egypt during the 18-day, anti-Mubarak uprising. Banks were closing early and most government departments were either closed for the day or were thinly staffed. Most schools and colleges are already closed for the summer holidays.

Thousands of Morsi's supporters have staged a sit-in since Friday in front of the Rabia al-Adawiya Mosque near the Ittihadiya presidential palace. In the evening, anti-Morsi crowds plan to march on the palace, and Morsi supporters have vowed to defend it if it is attacked.

The opposition protests emerge from a petition campaign by a youth activist group known as Tamarod, Arabic for “rebel.”

For several months, the group has been collecting signatures on a call for Morsi to step down. On Saturday the group announced it had more than 22 million signatures – proof, it claims, that a broad sector of the public no longer wants Morsi in office. It was not possible to verify the claim. Morsi's supporters have questioned the authenticity and validity of the signatures, but have produced no evidence of fraud. Morsi, who has three years left in his presidential term, claims that Mubarak loyalists are behind the planned protests. His supporters say Tamarod is a cover for thugs loyal to Mubarak.

The 22 million signatures, while they have no legal weight, deal a symbolic blow to Morsi at a time when he is widely seen by Egyptians to have failed to tackle the country's most pressing problems, from surging crime rates and high unemployment to fuel shortages and power outages.

If verified, the number of people who signed the petition calling on Morsi to step down would be nearly twice the number who voted for him a year ago in a run-off that he won with around 52 percent of the vote.