"The plan for them today is to march en masse towards the presidential palace; the show of force 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.
The opponents of the president hope to derail his plan and get 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.
Supporters of the president have vowed to confront the protesters to prevent them from reaching the presidential palace.
"That could end up being a recipe for some violence," Common said.
Elsewhere in Egypt, at least eight independent newspapers suspended publication Tuesday as part of a civil disobedience campaign.
Private TV networks are planning their own protest on Wednesday, when they could halt transmitting programs.
Morsi's laws appealed
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.Suggest a correction