EGYPTIAN Islamists brandishing swords clashed with opponents of a draft constitution in the city of Alexandria.
Tensions rose on the eve of a referendum on the disputed charter that has plunged the country into weeks of turmoil.
At least 19 people were reported injured in the violence, which broke out after an ultraconservative cleric urged worshippers to vote "yes" and described the opposition as "followers of infidels".
Thousands of Islamists filled a square in northern Cairo, raising pictures of President Mohammed Morsi, (pictured) who has insisted the referendum will begin today as scheduled despite accusations the entire process has been rushed. A few kilometres away, the opposition chanted for a "no" vote in a sit-in.
Religious authorities had issued orders that mosques should not be used to manipulate the vote, but several clerics, especially in conservative southern areas, took to the pulpit to tell their congregations that voting in favour of the constitution is seeking victory for Islam.
"Voting yes is like jihad for the sake of God," Sheik Abdel-Akher Hamad told worshippers in the southern city of Assuit. "It preserves Egypt from evils and from those who want to sabotage Islam and Muslims."
Most of Egypt's judges are refusing to monitor the vote, according to the Judges' Club union, although authorities said they would be able to meet the legal obligation to have a judge at each polling station.
More than 51 million people are registered to vote, with more than 6,000 polling stations in 10 provinces, including Cairo and Alexandria in today's first round.
"Polling stations can't open their doors unless there is a judge there," Zaghloul el-Blashi, the head of the referendum committee, told the pan-Arab TV station Al-Jazeera.
The Carter Center, the international group that has been monitoring Egyptian voting since last year's uprising, also said it would not deploy monitors for the referendum because of the government's late release of monitoring regulations.
The opposition coalition, The National Salvation Front, reiterated its call for Mr Morsi to postpone the referendum and draft a new constitution.