Almost everyone who cast ballots supported Egypt's new constitution in this week's referendum, results announced Saturday show, but a boycott by Islamists and low youth turnout suggest the country is still dangerously divided.

Nearly 20 million voters backed the new constitution, almost double the number of those who voted for one drafted in 2012 under the government of toppled Islamist president Mohammed Morsi. Only a narrow sliver of voters — 1.9 per cent — voted against the charter, after a massive government-sponsored campaign supporting it and the arrest of activists campaigning against it.

"Despite a milieu of intense social upheaval and acts of terrorism and sabotage that sought to derail the process, Egyptians have now marked yet another defining moment in our roadmap to democracy," presidential spokesman Ehab Badawy said. "The outcome represents nothing less than the dawning of a new Egypt."

The expected overwhelming support for the charter is seen as key to legitimizing Egypt's military-backed interim government, and the political plan put in place since Morsi's ouster in July. Analysts say it also suggests military chief Gen. Abdel-Fattah el-Sissi, who led the coup against Morsi, has enough popular support to make a rumoured run for the presidency himself.

It was the first vote since the military removed Morsi following massive protests in July. Hundreds celebrated in the streets after officials announced the results, including Hoda Hamza, a housewife who waved an Egyptian flag in Cairo's Tahrir Square and carried a picture of el-Sissi with an inscription reading: "By the order of the people, el-Sissi is president."

Hamza called the passage of the constitution a foregone conclusion.

Now, "I wish el-Sissi will be president," Hamza said. "We have no better man.... If it weren't for the army, we wouldn't have food on the table."

voter turnout 'unrivalled success'

Morsi supporters, who boycotted the vote, immediately challenged the results. Despite being outlawed and labelled a terrorist group, Morsi's Muslim Brotherhood and its allies continue to hold near-daily protests that often devolve into clashes with police.

"Even if 38 per cent of the voters took part, that still means that 62 per cent of the public rejects" the interim government, said Imam Youssef, a member of the Brotherhood's coalition against the July coup and an ultraconservative Islamist party. "They are trying to legitimize their coup."

The vote on the constitution was the first one since the military removed Egypt's first freely elected president, Mohammed Morsi, following massive protests in July. (Amr Nabil/Associated Press)

Egypt's High Election Commission said 38.6 per cent of the country's more than 53 million eligible voters took part in the two-day poll Tuesday and Wednesday. Judge Nabil Salib, who heads the commission, called the participation of 20.6 million voters an "unrivalled success" and "an unprecedented turnout."

In 2012, some 16.7 million voters cast ballots on the constitution drafted under Morsi, representing a 32.9 per cent turnout amid a boycott by liberal and youth groups. In that election, 63.8 per cent voted for the constitution.

Activists and monitoring groups have raised concerns over the atmosphere in which this new election took place. U.S.-based Democracy International, which had some 80 observers in Egypt, said a heavy security deployment and the layout of some of the polling stations "could have jeopardized voters' ability to cast a ballot in secret." It also said there was campaigning too close to the polling stations and a lack of nonpartisan domestic observers.

"There is no evidence that such problems substantially affected the outcome of this referendum, but they could affect the integrity or the credibility of more closely contested electoral processes in the future," the group said in a statement Friday.

In the lead up to the vote, police arrested those campaigning for a "no" vote on the referendum, leaving little room for arguing against the constitution.

U.S. Secretary of State John Kerry raised similar concerns in a statement, calling on Egypt's government to live up to its pledge to respect and expand rights while moving toward a civilian-led government through free and fair elections.

"Democracy is more than any one referendum or election," Kerry said.

Young voters stayed away

Government officials and pro-military commentators have suggested that the referendum's passage by a comfortable margin with a decent voter turnout would be viewed as legitimizing what el-Sissi has done since July, and a signal that people want him to run for president.

The general has not explicitly said whether he'll run.

"The link between the constitution and el-Sissi for president was symbolic," said Abdullah el-Sinawi, a commentator close to the military. "I think it is hard for him to say he won't run now and clash with a strong bloc (of 20 million) that calls for him to run. It would be like he's letting them down."

However, even Salib acknowledged young voters stayed away from the poll. He justified it by saying the vote coincided with midterm exams for university students.

El-Sinawi called it was a warning sign to authorities.

"This was a message that there is a crisis in reaching out to the new generation," he said.

Terrorist attacks surge

There has been an intense government crackdown on the Muslim Brotherhood and Morsi supporters since the coup, including the jailing of hundreds of its top leaders and the violent breakup of protests. Meanwhile, terrorist attacks surged in the restive Sinai Peninsula and some assaults reached Cairo and Nile Delta cities. On Saturday night, military officials said soldiers in a firefight killed Ahmed el-Manaei, a leading militant of Ansar Beit al-Maqdis, which has claimed many of the recent attacks.

The government has blamed the Brotherhood for the violence. The Brotherhood, which renounced violence in the late 1970s, denies being behind the attacks.

The constitution was drafted by a 50-member panel dominated by secular figures and appointed by the interim president. It limits the scope of Islamic law in the country's legislation, something Islamist groups enshrined in the 2012 constitution. It also ensures equality between women and men, and upholds the freedom of religion.

But with all its liberal clauses, the charter also gives the military the right to appoint its defence minister for the next eight years, and leaves its vast business holdings above oversight.