The city at the northern end of the Suez Canal has been a flashpoint since January, with violent protests over death sentences given to local people in connection with a football stadium riot in which more than 70 people died last year.
A court hearing is expected to confirm the death sentences handed down on 21 prisoners.
Youths wearing surgical masks, scarves and hoods threw stones and made lewd gestures at a line of police officers who released smoke bombs into streets strewn with rubbish, television footage from pan-Arab channel al-Arabiya showed.
"Karim Atout, 33, died from a gunshot to the head after doctors' efforts failed to revive him," Helmy Al-Affani, a local official of the health ministry in Port Said, told Reuters.
Law and order has deteriorated in Egypt since the overthrow of President Hosni Mubarak in a popular uprising two years ago, with some of the worst unrest in Port Said, an industrial city which residents complain has been neglected by central governments in Cairo.
At least seven people have been killed in this week's protests in Port Said - three security officials and four civilians.
The security services in the Mediterranean city told Reuters they were increasing protection of the central prison and Suez Canal Authority offices before the court ruling.
The clashes prevented some staff of a Suez Canal container company from going to work.
Underlining the overwhelming task facing authorities trying to restore order, police strikes spread across Egypt, with officers demanding better protection.
Hundreds of police refused to work for a second day at a base outside Ismailia, about 70 km (45 miles) south of Port Said, demanding more arms after several of their colleagues were killed in recent clashes.
Police also went on strike in Tanta, north of Cairo, while security forces charged with guarding one of President Mohamed Mursi's residences in the Nile Delta started a sit-in at a sports stadium to demand legal protection from prosecution over their actions to control civil unrest.
They said they did not want to get mixed up in the country's political crisis, state news agency MENA reported.
Dozens of police protested peacefully in Egypt's second city of Alexandria, saying they did not want their work to become politicised and chanting "the police are not against the people", MENA said. (Reuters)
