Egyptian officials say preliminary results indicate voters have endorsed the nation's military-backed constitution.
The outcome is seen as nudging army chief General Abdel Fatteh el Sissi closer to a bid for the presidency.
But violence surrounding the divisive referendum has left at least a dozen people dead, hundreds injured and hundreds more in jail.
Student supporters of Egypt's now banned Muslim Brotherhood chanted slogans against the country's interim government Thursday at Cairo University, as election officials tallied votes in the two-day referendum on a new constitution.
The vote comes six months after Egypt's military toppled the country's first democrqatically-elected President Mohamed Morsi in July after large protests against him and his government.
Initial reports show the new charter winning overwhelming approval of those who voted.
Final vote counts from around the country scrolled across the screens of Egyptian satellite channels throughout the day, showing “yes” votes in most districts of between 90 and 98 percent. Many analysts say the Muslim Brotherhood's decision to boycott the referendum may explain the lack of a significant “no” vote.
The new constitution, if it is approved, will replace a 2012 charter adopted during the year-long tenure of ousted Islamist President Morsi. The 2012 constitution was approved by more than 63 percent of those voting, but turnout was only 33 percent. Egyptian TV says at least half of Egypt's 51 million eligible voters turned out for the latest referendum.
One international monitor told Sky News Arabia that he and his team had “not seen any serious irregularities.”
A spokeswoman for Egypt's independent Ibn Khaldoun Center told a news conference the electoral commission had acted swiftly at reports of irregularities.
She says these included late openings at polling stations and impromptu closures for pretexts like eating and prayers.
Al Jazeera Direct, which secular political groups argue supports the Muslim Brotherhood, showed an amateur video in which it claimed to show the same person at a polling station voting more than once. VOA could not confirm the authenticity of the video.
Egypt's Interior Ministry indicated it had arrested more than 400 people, many of them Muslim Brotherhood supporters, for carrying weapons and other legal infractions during the referendum.
Authorities have been cracking down on the Brotherhood since Morsi's removal, declaring it a terrorist group and arresting many of its leaders. The former president and others are on trial for allegedly inciting violence. More than a 1,000 of pro-Morsi supporters have been killed in the crackdown.
People line up to vote in the Egypt's constitutional referendum in Cairo, Jan. 15, 2014.
A voter inks her finger after casting her ballot in a two-day constitutional referendum in Cairo, Jan. 15, 2014.
Election workers and ballot boxes are seen inside a polling station during a referendum on the new constitution in Cairo, Jan. 15, 2014.
Egyptians women show their inked fingers after casting their votes at a polling station in Cairo, Jan. 14, 2014.
Members of the Egyptian Interior Minister's security detail stand guard as voters line up at a polling station on the first day of voting in the country's constitutional referendum in the Zamalek neighborhood in Cairo, Jan. 14, 2014.
A woman holds a child as she casts her vote in the country's constitutional referendum in Hawamdaya, south of Cairo, Jan. 14, 2014.
Coptic Pope Tawadros II shows his ink-stained finger after voting in the country's constitutional referendum at a polling station in Cairo, Jan. 14, 2014.
A soldier stands behind a protective barrier of sand bags outside a polling station in Cairo, Jan. 14, 2014.
Supporters of the Egyptian Army and Army chief General Abdel Fattah el-Sissi hold posters and shout slogans in front of a damaged building of a court complex after an explosion in Imbaba, north of Cairo, Jan. 14, 2014.
A view of the front of a damaged building of a court complex after an explosion in Imbaba, north of Cairo, Jan. 14, 2014.
Egyptian editor and publisher Hisham Kassem said he was both pleased and surprised by the large turnout for the constitutional referendum, because he thought many Egyptians had grown disaffected by the numerous ballots since the 2011 revolution.
"I am delighted that political fatigue did not hit the bulk of the Egyptian people," said Kassem. "I was really concerned... that Egyptians would have given up on democracy by now. I went and voted myself, so I was standing there quietly listening to people. [The voting] was self-motivated."
Kassem indicated it would have been preferable if the interim government had allowed “more space for the 'no' campaign,” but he argued that campaigning by Muslim Brotherhood activists in recent months had raised emotions, ending with “excess violence.”
If approved, this week's referendum would be followed by elections for a new president and parliament. El Sissi - who removed Morsi from power last year - is widely seen as a presidential favorite.