Clashes have taken place Tuesday morning on Omar Makram Street near Cairo's Tahrir Square. Police used tear gas to disperse the protesters.
Some protesters formed a human shield between police and stone-throwing youth in Simon Bolivar Square to halt the violence. They also called on the youth, which numbered several dozen, to retreat to Tahrir Square where a mass protest will begin later today.
As of late morning, there was only one raised platform erected in Tahrir Square which was playing Quranic verses.
Opposition parties and groups have called for mass rallies across Egypt on Tuesday in protest at the President Morsi's recent Constitutional Declaration.
A sit-in has been ongoing in Tahrir Square since Friday against the declaration which protesters say gives the president "Pharaoh-like" powers.
Muslim Brotherhood has said it will not take part in protests called in support of the president's declaration. However, Muslim Brotherhood members in Alexandria have said they will take part in pro-declaration rallies in the coastal city.
Several Muslim Brotherhood offices were set on fire by protesters over the last week.