Police have fired tear gas in clashes with protesters gathered near the presidential palace in the Egyptian capital Cairo, according to local TV.
Some of the protesters were reported to have cut through barbed wire surrounding the palace.
Crowds had gathered to protest against recent decisions taken by President Mohammed Morsi.
They object to what they say was the rushed drafting of a new constitution, due to be voted on on 15 December.
A large protest was also reported to have gathered in Egypt’s second city Alexandria.
Activists have also been angered by a decree issued by Mr Morsi last month in which he awarded himself sweeping powers. He says he will give these up once a new constitution is ratified.