The referendum on the constitutional amendments is taking place over three days due to the increased number of eligible voters in the country, the head of Egypt's Election Authority Lasheen Ibrahim said on Friday.
More than 61 million Egyptians are eligible to vote in the referendum, Judge Lasheen said in an interview with Al-Ahram Daily.
Egyptians at home begin voting on Saturday, with polls closing for them on Monday.
Meanwhile, expatriates began voting at Egyptian embassies abroad on Friday, with polls closing for them on Sunday.
The current constitution was voted on in a two-day referendum in 2014.
Egyptians are voting on the proposed amendments to the 2014 charter, which were overwhelmingly approved by the parliament on Tuesday ,with 531 out of 596 members in favour, 22 against and one abstention.
On the presidency, the amendments include changing the length of presidential terms to six instead of four years under the 2014 charter.
They also extend the second term of President Abdel-Fattah El-Sisi, which is set to end in 2022, by two years, and allow him to run for the office for another term in 2024.
El-Sisi was first elected president in 2014 and was re-elected last year in a landslide victory where he secured 97 percent of the vote.
The amendments also allocate a quarter of the seats in parliament to women.
Around 20,000 judges will supervise the voting process at ballot boxes, and 55 local civil society groups, five foreign non-government organisations and three national councils will monitor the vote, Lasheen told Al-Ahram Daily.
Judge lasheen Ibrahim
Vote counting is scheduled to start at the end of the last voting day, on Monday.
The amendments would pass based on the absolute majority of valid votes, without requiring a quorum, per the constitution, Lasheen explained.
Those who back the changes say they are important for the stability of a country, and to allow the president more time to carry out his economic development plans. Critics say the changes will lead to increased presidential powers.
The Egyptian authorities have heightened security across the country ahead of the vote.
The interior ministry said it is adopting an extensive plan to "maintain security and order” and deal with any attempt to "disturb peace and security."
Those who will abstain from voting will be subject to existing laws that criminalize voting abstention, Lasheen said.
On Thursday, Egypt’s Religious Endowments Minister Mohamed Mokhtar Gomaa called on Egyptians to go to the polls, saying participation is a “national duty.”
The election authority has issued a number of regulations governing media coverage of the vote, including forbidding journalists from asking voters which way they are voting on the package of amendments.
Lasheen said the regulations are not meant to impose restrictions but rather to guarantee “a regular and smooth process.”
A special committee has been tasked with identifying violations.
Egyptians who live in governorates outside of their local election constituencies can still vote at special polling station reserved for out-of-governorate voters, according to Lasheen.
The election authority has set up special polling stations in industrial zones, in the under-construction New Administrative Capital Egypt east of Cairo, and at sites of other national megaprojects, to allow construction workers to vote.
New polling stations have also been set at Cairo International Airport and at major railway stations to draw more voters, and arrangements made at stations to accomodate citizens with special needs.
Egyptians living abroad began voting at diplomatic missions around the world earlier on Friday. They have until Sunday to cast their votes.
The amendments being voted on this weekend also give the president new powers to appoint members of the judiciary, and would create a second chamber of parliament, the Senate, with one-third of its members to be appointed by the president.
The amendments also assign the armed forces of the country the role of "safeguarding the constitution and democracy and the fundamental makeup of the country and its civil nature, the gains of the people and the rights and freedoms of individuals.”
They reintroduce the post of vice president, allowing the head of state to appoint one or more vice presidents, and allocate at least a quarter of the seats in parliament to women.