The deposed Islamist president's detention on Friday, under a court order for a renewable 15 days, further raised tensions as those applauding the decision and those demanding his reinstatement flooded parts of Cairo and other cities.
Five people were killed in the Mediterranean city of Alexandria in clashes between the rival protesters, despite a massive police and military deployment, the official Egyptian news agency reported.
The Arab world's most populous country has been rocked by violence that killed some 200 people since the army ousted Morsi on July 3, many in clashes between his supporters and opponents, and in militant attacks in the Sinai Peninsula.
At least 72 people were wounded in the Alexandria violence, in which riot police intervened. Ten people were wounded in clashes in Cairo, medics and the health ministry said.
The overwhelming number of Friday's marches remained peaceful, however, with tens of thousands of Morsi supporters gathering in a north Cairo square.
In Tahrir Square, a correspondent reported more than 100,000 anti-Morsi protesters gathered in response to a call from army chief General Abdel Fattah al-Sisi for Egyptians to show their support for a security clampdown on "terrorism".
Tens of thousands of army supporters also rallied outside the presidential palace, waving Egyptian flags and holding posters of Sisi who was Morsi's defence minister before ousting him.
A leader of Morsi's Muslim Brotherhood, Essam al-Erian, said in a statement that they would respond to his detention with "peaceful marches".
The accusations against Morsi include conspiring with Palestinian Hamas militants in attacks that killed policemen and staging prison breaks during the 2011 revolt that ousted president Hosni Mubarak.
Morsi had been detained with other Brotherhood leaders overnight on January 27, 2011, hours after the Islamist group said it would join the revolt against Mubarak. They later escaped from prison.
He is also accused of "premeditated murder of some prisoners, officers and soldiers, and kidnapping officers and soldiers," the Egyptian news agency said.


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