Sisi's supporters say the changes are necessary to give him more time to complete major development projects and economic reforms
Egyptians began voting on Saturday in a three-day referendum on constitutional changes that could allow President Abdel Fattah al-Sisi to stay in office until 2030 and bolster the role of the powerful military.
Sisi's supporters say the changes are necessary to give him more time to complete major development projects and economic reforms. Critics say they concentrate more power in Sisi's hands and return Egypt to an authoritarian model.
While the changes are expected to pass, observers say the turnout will be a test of Sisi's popularity, which has been dented by austerity measures since 2016. He was re-elected last year with 97% of the votes, on 41% turnout.
A double-decker bus blasting patriotic music circled around polling stations close to Cairo's Tahrir Square, the epicentre of the 2011 uprising that ended former President Hosni Mubarak's 30-year rule.
In the first hours of voting, people carrying flags and wearing T-shirts that said "do the right thing" - the slogan plastered on thousands of posters across the capital ahead of the vote - thronged round polling stations.
Polling stations open in #Egypt for a 3 day referendum over constitutional amendments that will allow Pres Sisi to rule until 2030, end the independence of the judiciary & name the Army the protector of the country. Last night Yes campaign #Tahrir, stolen from the revolutionaries pic.twitter.com/WZsI6NRZpk— Nuria Tesón (@masteson) April 20, 2019
They declined to comment on who had provided their campaign materials.
If approved, the amendments would extend Sisi's current term to six years from four and allow him to run again for a third six-year term in 2024.
They would also grant the president control over appointing head judges and the public prosecutor from a pool of candidates. They would task the military with protecting "the constitution and democracy and the fundamental makeup of the country and its civil nature".
"I believe that everything the president has done was for the good of the country, and I believe that we want the march to continue," Mona Quarashi, head of a local development NGO, said before she voted in downtown Cairo.
Tarek Badawi, a 40-year-old community organiser in the working class Shubra neighbourhood said he wanted to study the amendments before casting his ballot.
"There are some things I don't understand and I plan to sit with a relative today so he can explain them to me," Badawi told Reuters. "I'm not going to vote yes or no without understanding what's going on."
Opponents say the changes are being rushed through without proper public scrutiny. Officials say Egyptians from all walks of life were given a chance to debate the amendments, and that all views were factored into the final proposals.
"This is the final deathblow after all the ambitions we had after the 2011 revolution," said Khaled Dawoud, a member of the opposition Civil Democratic Movement.
Sisi came to power after spearheading, as defence minister, the removal of the Muslim Brotherhood's Mohamed Mursi as president in 2013. He was elected as president a year later and won the second four-year term last year.
Under Sisi, Egypt has witnessed a crackdown on dissent that rights groups say is unprecedented in its recent history. Media and social media are tightly controlled.
Lina Khatib, head of Chatham House's Middle East and North Africa Program, said the amendments "pave the way for a power grab" by Sisi.
"This has grave implications for prospects of democracy in Egypt in the medium term and makes it difficult for alternative political voices to contest power in the long term," she said.
Egypt's 596-member parliament, dominated by Sisi's supporters, approved the amendments on Tuesday, voting by 531 to 22 in favour.
Some 61 million of Egypt's nearly 100 million population are eligible to vote. The result is expected in the days after Monday's final day of voting.