At least one person was killed in Alexandria as protesters stormed a local Muslim Brotherhood office The US has warned Americans not to travel to Egypt and has told non-emergency diplomatic staff to leave, as clashes continued in the country. The state department also urged US nationals in Egypt "to remain alert".
The warning came as at least three people - including a US citizen - died in clashes between supporters and opponents of President Mohammed Morsi.
Tensions have been rising ahead of a mass rally planned by the opposition on Sunday, calling Mr Morsi to step down.
His supporters are stressing what they see as Mr Morsi's "legitimacy", rejecting the opposition's demand.
Sunday is the first anniversary of the president's inauguration.
In a warning on Friday, the state department said it had "authorised the departure of a limited number of non-emergency employees and family members" from Egypt. It asked Americans "to defer non-essential travel to Egypt at this time due to the continuing possibility of political and social unrest".
Cairo's main airport was packed with departing passengers, and all flights leaving for Europe, the US and the Gulf were fully booked, officials were quoted as saying.
The officials - who spoke on condition of anonymity - described the exodus as unprecedented, the Associated Press reports.
On Friday, two people died in the northern Egyptian city of Alexandria as protesters stormed an office of the Muslim Brotherhood - the political movement supporting President Morsi.
There are conflicting reports about how one of them - the US national - died.