Violence erupted in Port Said on Saturday after an Egyptian court handed down 21 death sentences in connection with the deadly riot last year at a football stadium in the Mediterranean city.

At least 74 people were killed in the riot on February 1, 2012, which began minutes after the final whistle in a game between al-Masry and the Cairo-based al-Ahly.

Al-Masry fans stormed the pitch after their team won, throwing stones, bottles and fireworks at al-Ahly supporters.

Witnesses said that police at the stadium did nothing to stop the violence, which set off days of violent protests in the capital Cairo.

The verdicts are not final; death sentences must be approved by Egypt's grand mufti, though that is largely a procedural formality. Defendants can also appeal their sentences, which could take years to carry out.

After the verdicts were handed down, the families of the defendants tried to storm the prison, and police used tear gas to disperse them.

There were reports of gunfire around the prison, with 30 people killed, including at least two police officers who were shot dead. Police have now sealed off Port Said, and the army has been deployed to "restore stability"; a curfew has been imposed in the area around the prison.

"It has been decided to deploy some units to work for calm and stability and the protection of public establishments," said General Ahmed Wasfi, in a statement carried by the official MENA news agency.

Al Jazeera's Rawya Rageh, reporting from the city, said that people in plainclothes were firing automatic weapons.

'Justice or blood'

Families of the victims inside the courtroom, meanwhile, reacted with joy and disbelief, cheering and holding pictures of their relatives. "The police are thugs," yelled relatives before the judge took the bench.

Hassan Mustafa, who had pinned a photo of his dead friend to his chest, said he was pleased with the verdict, but also wants "justice served for those who planned the killing."

The verdicts were also met with cheers by al-Ahly supporters who had gathered outside the football club in Cairo.

But the rulings will likely be seen as political - an effort to appease the "Ultras Ahlawy," die-hard supporters of al-Ahly, who threatened unrest in the capital if the rulings were not to their liking.

Al-Ahly supporters have blocked roads, bridges, and Cairo's metro system over the past few days. "Justice or blood," they warned in a statement on Facebook.

"There is nothing to say these people did anything, and we don't understand what this verdict is based on," one of the defendants' lawyers told the Associated Press by telephone. "[This was] a political decision to calm the public."

Dozens of other defendants, including security officials accused of failing to stop the violence, are expected to receive their verdicts on March 9.

All of this comes just hours after deadly protests that marked the second anniversary of the revolution that toppled longtime Egyptian ruler Hosni Mubarak.

Ten people were killed on Friday in anti-government protests in Suez and Ismailia, and more than 470 people were wounded; Mohamed Morsi, the Egyptian president, deployed the army in Suez to restore order.

Representatives of the National Salvation Front, the main opposition bloc in Egypt, held a press conference on Saturday to condemn the violence. The group demanded that Morsi appoint a new national unity government and form a committee to overhaul the recently-approved constitution, and threatened to boycott upcoming parliamentary elections unless its demands are met.