At least four people have been killed in Egypt and nearly 200 wounded in clashes between supporters and opponents of Islamist President Mohammed Morsi.
A crowd of more than 200,000 massed on Cairo's Tahrir Square in the largest demonstration since the 2011 uprising that overthrew President Morsi's predecessor, Hosni Mubarak.
More than 20,000 supporters of the Mr Morsi congregated outside a Cairo mosque not far from the main presidential palace where the much bigger opposition demonstration was taking place.
Hundreds of thousands of anti-government protesters marched through the Mediterranean port of Alexandria, Egypt's second city, and a military source reported protests in at least 20 towns around the country.
Four people were shot in Nile Valley towns south of Cairo, one in Beni Suef and three in Assiut, Reuters reports. Across the country, the Health Ministry said, 174 people were given medical treatment as a result of factional fighting in the streets.
Hundreds of people throwing petrol bombs and rocks attacked the national headquarters of Mr Morsi's Muslim Brotherhood. The building caught fire as guards and protesters exchanged gunfire.
Protesters accuse the president of failing to tackle economic and security problems since taking power a year ago.
The president's critics say the country's first Islamist president has put the agenda of the Muslim Brotherhood party ahead of the country's wider interests.
Mr Morsi was monitoring events from the heavily guarded Qubba presidential palace, where a presidency spokesman appealed for the demonstrations to remain peaceful.