Egyptian President Mohamed Morsi has cast his ballot for a controversial draft constitution that has sparked weeks of violence and protests.
Half of Egypt's eligible voters go to the polls Saturday. The rest of the country will vote December 22.
Officials said Saturday they have deployed 120,000 soldiers to protect polling stations, where long lines formed at many locations.
The proposed constitution has the support of President Morsi's former party, the Muslim Brotherhood. Mr. Morsi resigned from the group when he became president earlier this year.
Members of the liberal, secular and Christian opposition say they fear the constitution will erode civil liberties because it boosts the role of Islamic law and does not mention women's rights.
Clashes broke out Friday among stone-throwing demonstrators protesting the draft constitution near a mosque in Alexandria, prompting police to fire tear gas. Medical workers say 15 people were injured.
Also Friday in Cairo and other cities, thousands of flag-waving activists turned out for rival rallies. Such gatherings generally have been peaceful.
A largely Islamic committee approved the document last month after liberal and Christian members walked out, complaining they were being ignored.