The head of Egypt's army has given a TV address, announcing that President Mohammed Morsi is no longer in office.
Flanked by religious and opposition leaders, Gen Sisi said Mr Morsi had "failed to meet the demands of the Egyptian people".
Anti-Morsi protesters in Cairo gave a huge cheer in response to the speech.
But since the announcement, clashes have erupted in the northern city of Marsa Matrouh and at least four people have been killed.
The army's move to depose the president follows four days of mass street demonstrations against Mr Morsi - Egypt's first freely elected president - and an ultimatum issued by the military which expired on Wednesday afternoon.
Read more: BBC News - Egypt crisis: Army ousts President Mohammed Morsi