Voters turned out up in big numbers Saturday in most of the 10 Egyptian provinces where a first round of voting was held in a referendum on a disputed draft constitution amid allegations of mass irregularities, dpa reported.
With queues swelling polls, the election commission extended balloting time by four hours until 11 pm (2100 GMT).
Local TV networks showed live lines of voters still waiting at night to cast their ballots, braving low temperatures.
Monitors said the polling was marred by large violations, including mass voting, lack of full judicial oversight and illegal canvassing.
"All forms of fraud recorded in the era of (ousted President Hosny )Mubarak were seen again today," Hafez Abu Saada, a prominent human rights activist, told the privately owned Dream TV.
Mubarak was deposed almost two years ago.
Election commission chief Zaghloul al-Balshi denied allegations that the voting was not fully overseen by judges.
"We will verify all complaints to determine their impact on the integrity of the process," he told a press conference late Saturday.
He said that the result would be officially announced after the second and final round to be held on December 22.
Vote counting began late Saturday after the end of polling with preliminary results showing a tilt toward endorsing the referendum, local media reported.
President Mohammed Morsi's Muslim Brotherhood and its Islamist allies have campaigned heavily for the draft constitution, arguing that it is necessary to fast-track the transition from Mubarak's authoritarian rule.
The opposition says the charter, drafted by an Islamist-led constituent assembly, could undermine women's and political rights and sideline minorities.
"I don't like an Islamic system in control of my country because I know Morsi is a dictator - he controls my life and my family. I prefer liberation," Naier al-Guindy, 59, told dpa at a Garden City polling station in central Cairo.
Hinar Sabry, a 25-year-old veiled girl, said she would vote for the charter.
"The articles that the people think are controversial are really not that controversial - they're just making a big fuss about it on TV," she said.
"It's more of a political stand for the opposition. The opposition just wants power, and they don't really care about what the constitution says."
Tens of thousands of army and security personnel were deployed outside polling stations to maintain order.
"The long lines of voters at polls are the best answer to those who called for boycotting or postponing the referendum," senior Brotherhood official Essam al-Erian said in a tweet.
Nobel Peace laureate Mohammed ElBaradei, who leads the opposition coalition National Salvation Front, urged a "No" vote. He had earlier called on Morsi to postpone the referendum, warning of a possible civil war.
Divisions over the constitution have sparked deadly protests and attacks on several Brotherhood offices.
The main office of the liberal al-Wafd Party and its mouthpiece in the Cairo area of Dokki were attacked Saturday.
The party's officials blamed the attack on hardline Islamists, claiming that the assailants had sought to "intimidate" al-Wafd for its opposition to the draft constitution.
The voting on the charter had to be spread across two days after many of Egypt's judges refused to oversee the balloting because of the constitution's perceived curbs on freedoms. Without judicial supervision, the vote would be considered illegal.
About 25.8 million Egyptians were eligible to vote in the first round of the polls, according to government figures.
The final result is to be determined by the majority of the valid ballots cast in both rounds.
If the draft constitution is voted down, Morsi will call an election within three months to pick a new constituent assembly.