CAIRO -- A court sentence in the death of 74 fans at a Port Said soccer stadium set off the deadliest round of protests in Egyptian President Mohammed Morsi’s five-month tenure Saturday and a surge violence around the country that showed no signs of subsiding.

As the day wore on, it appeared that Egypt was headed into a period of prolonged instability, as each clash between protesters and security forces seemed to build on one another. By mid-afternoon, Port Said clashes spread to parts of Cairo, including at the Ministry of Interior, subway stops and the city’s main bridges.

A day earlier, at least seven were killed in Suez in clashes between police and protesters on the two-year anniversary of the uprising that led the fall of former Egyptian leader Hosni Mubarak and the promise of a renewed Egypt. On Saturday, such hopes seemed like a distant memory. Instead, many Egyptians feared Saturday’s violence between two rival soccer teams and their supporters could lead to fans traveling between Cairo and Port Said in retaliations and counter-retaliations.

By evening it appeared Egypt was locked in a deadly cycle of violence that neither the civilian government nor police could stop. Saturday’s deadly protests, which killed at least 30, including two police officers, were set off by a death sentence for 21 in the Feb. 2012 death of 74 soccer fans at a Port Said stadium.

The Minister of Interior called the Port Said violence “unprecedented” in the history of the northern city, Egypt’s fifth largest. Most Port Said shop owners closed down for the day, and Egyptian railways refused to stop in Port Said for fear of getting stuck in the violence.

In Cairo, the city streets were empty but for hundreds of protesters clashing the police in tit-for-tat battle. Protesters, many donning facemasks, threw rocks and Molotov cocktails as they ran away from police throwing scores of cans of tear gas. The odious smell was so palatable that commuters on the city’s subways had to cover the faces.

In Tahrir Square, the iconic scene of the 2011 uprising that led to the overthrow of former Egyptian President Hosni Mubarak, a cloud of fumes hung over the air from both the gas and a school building set ablaze nearby.

A long-awaited court ruling set off Saturday’s violence. In February 2012, after Port Said’s al-Masry soccer team won in a 3-1 upset to visiting Cairo al-Ahly team, fans stormed the field. Many in the crowd panicked and ran toward the locked door. In the mayhem, 74 died, largely al-Ahly supporters, making it the deadliest attack on an Egyptian sports event.

In what was expected to be a controversial ruling, the courts ruled Saturday morning that 21 to be executed for their role in the killing of the fans. The courtroom, dominated by the families of those killed, erupted into a flurry of emotion even as it was unclear what role the 21 people played in the stampede. One lawyer said that none of those sentenced were police officers but rather fans at the stadium.

In Port Said, there appeared to be shock that local fans were sentenced for the death of an arch-rival team’s fans as many hold al-Ahly fans responsible. As families gathered in front of the Port Said prison holding the 73 defendants, including five police commanders, they threw rocks. The police responded with tear gas and eventually gunfire, leading to the deaths. In a video posted on a state website’s newspaper, as protesters fled gunfire, rocks and tear gas, they cursed the government. Another 350 were injured, including 150 police officers, the Ministry of Health said.