Discontent in Egypt has spread to Cairo, where stone and bottle-throwing youths have taken to the streets.
Police and demonstrators have clashed in the area surrounding Tahrir Square after the funeral of a protestor who died after unrest in January.
Egypt has been in political turmoil since the president, Hosni Mubarak, was ousted by a popular revolution in 2001.
In Port Said, security forces battled bottle-throwing youths for the third night running.
At least 50 people were wounded.
Security forces fired into the air and used tear gas on protestors gathered in front of a local government building in the city, which has become the focus of their discontent.
Port Said has seen waves of violent demonstrations since January over the detention of dozens of people in connection with a soccer riot last year in which more than 70 died.