Opponents of constitutional amendments that could see Egypt's President Abdel Fattah al-Sisi stay in power until 2030 urged people to vote "no" on Monday, the third and final day of a referendum on the proposal.
The amendments would also bolster the role of the military and expand the president's power over judicial appointments. The constitutional changes were approved by parliament last week.
While the amendments are expected to be passed in the referendum, 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 percent of votes cast.
Sisi's supporters say he has stabilized Egypt and needs more time to reform and develop the economy. Critics fear changing the constitution will shrink any remaining space for political competition and debate, paving the way for a long period of one-man rule.
Ahmed al-Tantawi, one of a small number of opposition members of parliament, said the referendum was being held against a backdrop of intimidation and "vote buying".
The electoral commission said on Monday afternoon it had not received any formal complaints so far about any irregularities.
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"We can say that the first two days of voting were held under the slogan, the 'ticket and the cardboard box'," Tantawi said, referring to reports that grocery boxes were being handed out to people in exchange for casting a vote.
"But there is a chance on the third day of voting for Egyptians, particularly the youth, to return things to their natural course," he said.
Activists have posted photos on social media that appeared to show white cardboard boxes packed with groceries being handed out to people after they voted.
A Reuters reporter saw some voters receiving vouchers for groceries after leaving a central Cairo polling station, which they then exchanged for packages of cooking oil, pasta, sugar and tea at a nearby charity.
It was not immediately possible to verify who was distributing the food.
When asked about the boxes, Mahmoud el-Sherif, spokesman for Egypt's election commission, said it was monitoring for any violations. But he added: "The commission has received no notifications or complaints of this kind so far."
The commission says it has strict measures to ensure a fair and free vote, posting judges at each polling station and using special ink to prevent multiple voting.
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, and give Egypt's powerful military the role of protecting "the constitution and democracy".
Cairo's streets have been adorned with banners encouraging people to vote, some of them backing a "yes" vote.
Ahmed Maher, a founder of the April 6 Movement, one of the youth groups behind the 2011 uprising that toppled President Hosni Mubarak, said Egyptians still had a chance to make their voice heard.
"Try to change the result, even by a small ratio," he wrote in a message posted on social media. "Tell your relatives, friends and acquaintance to go down and say 'No'."
Some 61 million of Egypt's nearly 100 million population are eligible to vote. The result is expected within five days.