Tens of thousands of opponents of Egypt's Islamist president have massed in Cairo's Tahrir Square, launching an all-out push to force Mohammed Morsi from office.
Fears of violence on the one-year anniversary of his inauguration are high, with Morsi's Islamist supporters vowing to defend him.
Waving Egyptian flags, crowds packed Tahrir, the birthplace of the 2011 uprising that toppled autocrat Hosni Mubarak, and chants of "erhal!", or "leave!" rang out.
On the other side of Cairo, thousands of Islamists gathered in a show of support for Morsi outside the Rabia al-Adawiya Mosque near the Ittihadiya presidential palace, which the opposition planned to march on in the evening.
Some Morsi backers wore homemade body armour and construction helmets and carried shields and clubs - precautions, they said, against possible violence.
There is a sense among opponents and supporters of Morsi that Sunday is a make-or-break day, hiking worries that the two camps will come to blows, even as each side insists it won't start violence.
Already at least seven people, including an American, have been killed in clashes the past week, mainly in Nile Delta cities and the coastal city of Alexandria.
The demonstrations are the culmination of polarisation and instability that have been building since Morsi's June 30, 2012 inauguration as Egypt's first freely elected leader. The past year has seen multiple political crises, bouts of bloody clashes and a steadily worsening economy, with power outages, fuel shortages, rising prices and persistent lawlessness and crime.
The opposition believes that with sheer numbers in the street, it can pressure Morsi to step down - perhaps with the added weight of the powerful military if it signals the president should go.
Asked by The Guardian whether he was confident that the army would not intervene if the country becomes ungovernable, Morsi replied, "Very".