Underlining the tension, some 120,000 army troops were deployed to help the police protect polling stations and state institutions after clashes between Morsi's supporters and opponents over the past three weeks left at least 10 people dead and about 1,000 wounded. The large-scale deployment did not stop a mob of supporters of ultraconservative cleric Hazem Salah Abu-Ismail attacking the Cairo offices of the liberal Wafd party, a member of an opposition alliance that has campaigned against the draft constitution.
"Today I would like to offer my condolences to the Egyptian people on the collapse of the rule of law," Wafd leader El-Sayyed el-Badawi said.
The opposition called for a "no" vote, while Morsi's supporters said the constitution will help end the political instability that has roiled Egypt since the autocratic Mubarak was overthrown. Clerics, from the pulpits of mosques, have defended the constitution as a document that champions Islam.
The draft would empower Islamists to carry out the most widespread and strictest implementation of Islamic law that modern Egypt has seen. That authority rests on the three articles that explicitly mention Shariah, or Islamic law, as well as obscure legal language buried in a number of other articles that few noticed during the charter's drafting but that Islamists insisted on including.
According to both supporters and opponents of the draft, the charter not only makes Muslim clerics the arbiters for many civil rights, it also could give a constitutional basis for citizens to set up Saudi-style "religious police" to monitor morals and enforce segregation of the sexes, imposition of Islamic dress codes and even harsh punishments for adultery and theft regardless of what the laws on the books say.
For Islamists, the constitution is the keystone for their ambitions to bring Islamic rule, a goal they say is justified by their large victory in last winter's parliamentary elections. Morsi rejected opposition demands that he cancel the referendum.
When voting day finally arrived, the anger and frustration of the past three weeks remained and scenes of voters hotly debating the cons and pros of the constitution or countering each other's take on Morsi, the Brotherhood, the Salafis or reform leader Mohamed ElBaradei were common.
"Those who wrote the constitution are God-fearing men," Mohammed Hassan el-Khatab, a bearded 52-year-old government employee, yelled as he stood in line outside a polling center in the Mediterranean port city of Alexandria.
"Those opposed to the constitution are just noisy, they have no popular base. Let the people decide," said el-Khatab, whose support for the draft is typical in his low-income el-Siouf district, home to a mix of Christian, Muslim Brotherhood supporters and Salafis.
Girgis Bakheet, a 56-year-old Christian decorator, overheard el-Khatab and decided to weigh in on the debate with an instant dismissal of the notion that being God-fearing is a qualification for writing a constitution.
"This is a constitution that is stillborn. It doesn't represent all people. Arguing that it observes God's laws is a good thing, but only on the face of it. God has nothing to do with constitutions and elections," he said.
Mohammed Hudhaifa, 41 and a school teacher with a light beard, told Bakheet he should not offend Muslim beliefs.
"I am a Muslim whose religion is a way of life that deals with every little and big thing," he said. The constitution, he continued, gives Christians freedom to worship, "But I will not accept that you tear my religion to shreds," he angrily told Bakheet. Feeling threatened by the chorus of endorsement Huddhaifa earned from fellow Muslims in the line, Bakheet bowed out.
"I took part in this revolution and got injured. If I knew it would come to this, I wouldn't have participated," he said as he walked away from the hostile crowd.
In Cairo's central and densely populated Sayeda Zeinab district, home to a much revered Muslim shrine, 23-year-old engineer Mohammed Gamal said he was voting "yes" although he felt the proposed constitution needed more, not less, Islamic content.
"Islam has to be a part of everything," said Gamal, who wore the mustache-less beard that is a hallmark of hardline Salafi Muslims.
Flight attendant Iman Naguib Mahfouz, a Christian, had a different take on the crisis, speaking kilometers (miles) away in Nasr City, a district in eastern Cairo that is a Brotherhood stronghold.
"I am a Christian and either way we are living in a Muslim state," she said. "But this president is not representing Egyptians, he's representing the Muslim Brotherhood."
Critics, meanwhile, are questioning the charter's legitimacy after the majority of judges said they would not supervise the vote. Rights groups also warned of opportunities for widespread fraud, and the opposition said a decision to hold the vote on two separate days Dec. 15 and 22 to make up for the shortage of judges left the door open for initial results to sway voter opinion in the next round.
The Muslim Brotherhood began to issue partial results based on its own exit polls late Saturday. They showed the "yes" vote to be ahead.
The shortage of judges was reflected in the chaos engulfing some polling stations, which led the election commission to extend voting by four hours until 11 p.m.
The violations reported by monitors included polling centers without judges to oversee the process, civil employees illegally replacing the judges, ballot papers not officially stamped as per regulations, campaigning inside polling stations and Christian voters being turned away.
Mohammed Ahmed, a retired army officer from Cairo, said bearded men he suspects of being Muslim Brotherhood members were whispering "vote yes" to men standing in line outside a polling center in Cairo's poor district of Arab el-Maadi.
"The Brotherhood wants to turn Egypt into its own fiefdom," he claimed.
Egypt has 51 million eligible voters, half of whom were supposed to cast their ballots Saturday in 10 provinces, and the rest next week.
"I am definitely voting no," Habiba el-Sayed, a 49-year-old housewife who wears the Muslim veil, or hijab, said in Alexandria. "Morsi took wrong decisions and there is no stability."
Another female voter in Alexandria, 22-year-old English teacher Yomna Hesham, said she was voting 'no' because the draft is "vague" and ignores women's rights.
"I don't know why we have become so divided ... Now no one wants to look in the other's face," said Hesham, who also wears the hijab, after voting. "This will not end well either way. It is so sad that we have come to this."
Egypt's latest crisis began when Morsi issued a decree on Nov. 22 giving himself and the assembly writing the draft immunity from judicial oversight so the document could be finalized before an expected court ruling dissolving the panel.
On Nov. 30, the document was passed by an assembly composed mostly of Islamists, in a marathon session despite a walkout by secular activists and Christians from the 100-member panel.
The schism caused by the crisis was on display when a powerful member of the Brotherhood, Khairat el-Shater, went a Cairo polling center to vote. Women standing in line yelled insults at him and his group, calling him a dog and a liar. El-Shater was the Brotherhood's first choice for a presidential candidate but a Mubarak-era conviction disqualified him, allowing Morsi to take his place.
In Alexandria, a group of women complained that a judge with suspected Brotherhood links intentionally stalled the process to prevent them from voting by taking long breaks to eat, pray and talk on the phone. Angry and frustrated, the women blocked the street outside the polling center.
Cairo businesswoman Olivia Ghita also criticized the constitution as being tailored for the Brotherhood.
"At one point in our history, Cleopatra, a woman, ruled Egypt. Now you have a constitution that makes women not even second-class but third-class citizens," said Ghita.
If the constitution is approved by a simple majority of voters, the Islamists empowered when Mubarak was ousted would likely gain more clout. The upper house of parliament, dominated by Islamists, would be given the authority to legislate until a new parliament is elected.
If it is defeated, elections would be held within three months for a new panel to write a new constitution. In the meantime, legislative powers would remain with Morsi.