Egyptian police fired tear gas to stop demonstrators who broke through a security blockade near the presidential palace as hundreds of thousands of people took to the streets of Cairo to protest the country's Islamist leader.

Crowds around the capital and in the coastal city of Alexandria were still swelling several hours after nightfall on Tuesday. The large turnout signalled sustained momentum for the opposition, which brought out at least 200,000 protesters to Cairo's Tahrir Square a week ago and a comparable number on Friday. They are demanding that President Mohammed Morsi rescind decrees that placed him above judicial oversight.

In a brief outburst, police fired tear gas to stop protesters approaching the palace in the capital's Heliopolis district. Morsi was in the palace conducting business as usual while protesters gathered outside. But he left for home through a back door when the crowds "grew bigger," according to a presidential official who spoke on condition of anonymity because he was not authorized to speak to the media.

The official said Morsi left on the advice of security officials at the palace and to head off "possible dangers" and to calm protesters. Morsi's spokesman, however, said the president left the palace at the end of his work schedule through the door he routinely uses.

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Former Egyptian presidential candidate Khaled Ali (C) shouts political slogans outside of the presidential palace in Cairo on Tuesday. (Gianluigi Guercia/Agence France-Presse)

The violence erupted when protesters pushed aside a barricade topped with barbed wire several hundred metres from the palace walls. With that barricade removed protesters moved closer to the palace walls.

The brief outburst of violence left 18 people injured, none seriously, according to MENA, the official Egyptian news agency.

Protesters also commandeered two police vans, climbing atop the armoured vehicles to jubilantly wave Egypt's red, white and black flag and chant against Morsi. Nearly two hours into the demonstration, they were mingling freely with the black-clad riot police, with many waving the flag and chanting against Morsi.

Protesters are angered over Morsi's almost unrestricted powers and a proposed new draft constitution that was hurriedly adopted by his allies last week.

"The show of force is intended as a last-ditch effort to get Morsi to abandon his plans for a referendum on a new constitution that's to be held in less than two weeks now," CBC's David Common reported from the scene.

'Freedom or we die'

"Freedom or we die," chanted a crowd of several hundred outside a mosque in the Abbasiyah district. "Mohammed Morsi! Illegitimate! Brotherhood! Illegitimate!" they also yelled, alluding to the fundamentalist Muslim Brotherhood from which Morsi hails.

"This is the last warning before we lay siege on the presidential palace," said Mahmoud Hashim, a 21-year-old student from the city of Suez on the Red Sea. "We want the presidential decrees cancelled."

The protests were dubbed "The Last Warning" by organizers amid rising anger over the draft charter and decrees issued by Morsi giving himself sweeping powers that placed him above judicial oversight. Morsi called for a nationwide referendum on the draft constitution on Dec. 15, but the opposition has called on him to launch a new inclusive constitutional process.

"They feel that Islamists have dominated it, [and] that others like moderates and Christians have had no role in deciding what future Egypt will have under its new constitution," Common said.  

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Anti-Morsi protesters remove barbed wire during clashes with riot police in front of the presidential palace in Cairo, on Tuesday. (Amr Abdallah Dalsh/Reuters)

In Alexandria, some 10,000 opponents of Morsi gathered in the centre of the country's second largest metropolis. They chanted slogans against the leader and the Muslim Brotherhood.

It is Egypt's worst political crisis since the ouster nearly two years ago of authoritarian president Hosni Mubarak. The country has been divided into two camps: Morsi and the Brotherhood, as well as ultraconservative Salafi Islamists, versus youth groups, liberal parties and large sectors of the public.

Morsi, who narrowly won the presidency in a June election, appeared to be in no mood for compromise.

A statement by his office said the Egyptian leader met on Tuesday with his deputy, prime minister and several top cabinet members to discuss preparations for the referendum. The statement appeared also to suggest that it is business as usual at the presidential palace despite the rally outside its doors.

The Islamists responded to the mass opposition protests last week by sending hundreds of thousands of supporters into Cairo's twin city of Giza on Saturday and across much of the country. Thousands also besieged Egypt's highest court, the Supreme Constitutional Court.

The court had been widely expected Sunday to declare the constitutional assembly that passed the draft charter on Friday illegitimate and to disband parliament's upper house, the Shura Council. Instead, the judges went on strike after they found their building under siege by protesters.

Morsi's laws appealed

Elsewhere in Egypt on Tuesday, at least eight independent newspapers suspended publication as part of a civil disobedience campaign.

Private TV networks are planning their own protest on Wednesday, when they could halt transmitting programs.

Judges have already gone on strike over Morsi's decrees made Nov. 22 that placed him above any form of oversight, including the courts.

Under Morsi's new powers, which he has claimed are temporary, any laws he has made since he took office back in June and any laws in the immediate future are final, and cannot be appealed to the judiciary until a new constitution is approved.

The new president also barred any court from dissolving the upper house of parliament, where Islamists are the majority, or the constituent assembly,

Egypt's proposed new constitution, which was drafted by a panel of Islamists, has come under fire for not protecting the rights of women and minority groups. Journalists also say it restricts freedom of expression, while other critics say it will give Islamic clerics a say in legislation.

With files from CBC News