The BBC's Jon Leyne says that a number of injuries among the protesters have been reported
Police have fired tear gas in clashes with tens of thousands of protesters gathered near the presidential palace in the Egyptian capital Cairo.
Some of the protesters reportedly cut through barbed wire around the palace.
Crowds have been gathering to protest against what they say is the rushed drafting of a new constitution and the decision by President Mohammed Morsi to extend his powers.
Mr Morsi was in the palace but left as the crowds grew, sources there said.
As well as the protest outside the presidential palace in the suburb of Heliopolis, thousands of demonstrators have gathered in Cairo's Tahrir Square.
A sizeable crowd has also turned out in Egypt's second city Alexandria.
Several newspapers refused to go to press on Tuesday in protest at what they say is the lack of press freedom in the constitution.
Mr Morsi adopted sweeping new powers in a decree on 22 November, and stripped the judiciary of any power to challenge his decisions.
He has also called a nationwide referendum for 15 December on a new constitution, which opponents say has been rushed through and fails to protect the rights of minorities, particularly women.
Mr Morsi, who narrowly won Egypt's first free presidential election in June, says he will give up his new powers once a new constitution is ratified.
His actions have brought out thousands, both his supporters and his opponents, in recent days.
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