Lines of black-clad officers kept apart thousands of Islamists on one side and hundreds of anti-constitution protesters on the other. Dozens of rival protesters pelted each other with rocks in running battles.
The violence broke out on the eve of the final round of a referendum on the draft charter, which is backed by President Mohammed Morsi and his Islamist supporters.
Alexandria, which voted in the first round of the referendum last weekend, has seen several clashes between pro- and anti-Morsi protesters.
On 14 December, opposition protesters besieged a mosque in the Mediterranean city, prompting running battles between rock-throwing groups of men, some of whom brandished swords.
Islamists organised Friday’s rally to protest last week’s siege of the mosque, sparked by a cleric’s call for people to vote yes in the constitution.
Duelling demonstrations have been taking place around Egypt for a month. On 5 December, vicious clashes broke out in front of Morsi’s presidential palace in Cairo, killing eight people and wounding more than 600.
The army has deployed 120 000 soldiers to bolster 130 000 police tasked with maintaining security during the volatile voting.
The opposition sees the proposed constitution as weakening human rights and opening the way to creeping sharia-style strict Islamic laws under Morsi.- SAPA