Egyptians began voting on Saturday in a two-round referendum on a new constitution supported by the ruling Islamists but bitterly contested by a secular-leaning opposition that has waged weeks of protests.
President Mohamed Morsi's determined push to see through the draft charter led to street clashes in Cairo last week between the rival camps, with eight people killed and hundreds injured.
More clashes broke out on the eve of the referendum in Alexandria, Egypt's second biggest city.
Rock-throwing mobs confronted each other late on Friday after a cleric urged worshippers in his mosque to support the constitution, resulting in more than 15 people hurt. Police used tear gas after some protesters fired birdshot.
By early Saturday, calm had returned to the city, AFP correspondents said.
Egypt's vote will be staggered over two rounds to ensure there will be enough judges to monitor polling stations amid a rift within the judiciary over the referendum process.
Polls on Saturday opened in Cairo, Alexandria and eight other provinces and are scheduled to close at 7:00 pm. The rest of the country votes on December 22.
The first round's unofficial results are expected hours after polling ends.
Morsi cast his ballot at a polling station near the presidential palace in Cairo, state television showed. He made no comment to the media.
The president has ordered the military to help police maintain security until the results are known. A total of 130,000 police and 120,000 soldiers are being deployed, interior ministry and military officials told AFP.
Morsi's Muslim Brotherhood has thrown its formidable organisational machine behind a campaign in favour of the draft constitution.
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"I'm voting for stability and for Dr Morsi's promised programme of renewal. I have gone over the text to compare it with what the opposition is saying, and what they say is false. It's a good constitution," said one Cairo voter, Enayat Sayyed Mostafa, a retired woman.
Ramona Garras, a 60-year-old Christian woman, said the referendum was "a matter of democracy," adding: "If the government ensures democracy, then we will support it."
The main opposition coalition, the National Salvation Front, is urging a massive "no" vote to the draft charter, which it sees as weakening human rights, especially for women and religious minorities.
Many of its supporters were especially hostile to the Muslim Brotherhood, which it believes wants to usher in sharia-style (strict Islamic) laws.
"I'm voting because I hate the Muslim Brotherhood, it's very simple. They are liars," said one voter, Abbas Abdelaziz, a 57-year-old accountant, outside a Cairo polling station.
Ali Mohammed Ali, an unemployed 65-year-old wearing a traditional long robe, said: "I voted for Morsi and it was a mistake, a big mistake. This constitution is bad, especially because it doesn't forbid child labour and opens the way for the marriage of minors."
Nagat Radi, a veiled woman in her 50s, said many articles in the draft constitution were problematic "and will hurt our country and our children."
She added: "The people are going in one direction and the Brothers in another. Those voting 'yes' believe it is a gesture of piety and obedience to the president."
International watchdogs, including the UN human rights chief, and the United States and European Union have expressed reservations about the draft because of loopholes that could be used to weaken human rights, including those of women, and the independence of the judiciary.
Analysts said it was likely -- but not certain -- the draft constitution would be adopted.
"If the constitutional draft is approved by less than 60 percent of the voters, it may become a linchpin for future disputation over the validity of the political system that springs from it," Yasser El-Shimy, a Middle East analyst for the International Crisis Group, told AFP.
"If more than 60 percent vote yes, it would be very hard for the opposition to claim that they represent the preferences of the Egyptian people at large," he said.