Supporters of President Mohamed Mursi and his opponents hurled rocks at each other in Egypt's second city on the eve of a final vote on an Islamist-influenced constitution that has divided the country.
Police fired tear gas to separate scores of opponents of the constitution and thousands of Islamists who clashed in the rain near a mosque in Alexandria on Friday. Health officials said 32 people were injured.
"God is great," Islamists chanted as the clashes began.
The Islamists had gathered in support of an Islamic vision of Egypt's future a day before a second round of voting in a referendum on the basic law. Opposition supporters had also turned out as worshippers assembled for Friday prayers.
Mursi and his Islamist allies back the draft constitution as a vital step in Egypt's transition to democracy almost two years after the fall of Hosni Mubarak.
The opposition says the draft, drawn up by an Islamist-dominated assembly, is a recipe for deeper divisions and more violence.
The Muslim Brotherhood called for the rally in Alexandria to protest after a violent confrontation between Islamists and the liberal, secular opposition last week ended with a Muslim preacher besieged inside his mosque for 14 hours.
Rival factions had used clubs, knives and swords last week, but this time police kept the feuding sides apart, although witnesses saw several protesters and one police officer being helped away. Some protesters had head wounds.
The run-up to the final round of voting on the new constitution on Saturday has been marked by often violent protests that have cost at least eight lives. The first round on December 15 produced a "yes" vote that is expected to be repeated in the second round.
Lines of riot police cordoned off Alexandria's al-Qaid Ibrahim mosque, scene of last week's violence. Islamists chanted pro-Islamic slogans while a smaller group of opponents gathered nearby, chanting against Mursi, propelled to power in a June election by the Muslim Brotherhood.
Two city buses were set on fire outside Alexandria University's medical faculty, sending up a big plume of black smoke amid further sporadic street clashes.
"The people want the implementation of sharia," the Islamist sympathizers shouted, in a show of support for Islamic law. "Our souls and blood, we sacrifice to Islam," they shouted.
In one incident, an Islamist filming anti-Mursi protesters was grabbed and roughed up. Islamists on the other side of a security cordon pushed and shoved police trying to reach him.
The opposition, facing defeat in the referendum, has called for a "no" vote against a document it says is too Islamist and ignores the rights of women and minorities, including the 10 percent of Egyptians who are Christian.
Anti-Mursi protester Ali al-Banna, a 51-year-old businessman, said: "We reject the constitution. Mursi's legitimacy has collapsed and we will bring him down."
The first day of voting on December 15 resulted in a 57 percent majority in favor of the constitution. The second stage on Saturday is expected to produce a similar result as it covers regions seen as more conservative and likely to back Mursi.
The National Salvation Front, the main opposition coalition, said a "no" vote meant taking a stand against attempts by the Brotherhood to dominate Egypt.
The constitution must be in place before a parliamentary election can be held. If it passes, the poll should be held within two months.
Demonstrations erupted when Mursi awarded himself sweeping powers on November 22 and then fast-tracked the constitution through a drafting assembly dominated by his Islamist allies and boycotted by many liberals.
The referendum is being held over two days because many of the judges needed to oversee polling stayed away in protest. In order to pass, the constitution must be approved by more than 50 percent of those voting.