A daily curfew from 21:00 to 06:00 will be imposed for 30 days beginning on Monday, also covering Suez and Ismalia, he said in a TV speech to the nation.
At least 33 people have been killed in unrest over the weekend.
Protests erupted after a court sentenced 21 local people over deadly football violence nearly a year ago.
Mohamed Morsi said he mighty take further steps “for the sake of Egypt” as it was his “duty” as president.
He also invited political leaders to a “national dialogue” on Monday.
In the capital Cairo, anti-government protesters clashed with security forces near Tahrir Square for a fourth consecutive day.
The liberal opposition accuses Mohamed Morsi of being autocratic and driving through a new constitution that does not protect adequately freedom of expression or religion.
The government is also being blamed for a deepening economic crisis.
Correspondents say Port Said remains in a state of rage after the 21 defendants were sentenced over riots which killed 74 people after a football game last February.
February’s violence began when fans of Port Said side al-Masry attacked visiting supporters from Cairo club al-Ahly.
Fans flooded on to pitch attacking al-Ahly players and fans as the match ended.
Most of the victims died of concussion, cuts and suffocation.
About 30 people were killed in unrest in the city on Saturday with a further three dying at a mass funeral on Sunday.
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