Supporters and opponents of Egypt's president are staging final rallies ahead of a referendum on a draft constitution, due to start on Saturday.
Opponents say the draft document has been crafted poorly and without proper consultation, and is too Islamist.
President Mohammed Morsi insists the constitution is needed to complete the transition from Hosni Mubarak's rule.
The controversy has sparked unrest across Egypt and fresh clashes have broken out in Alexandria.
'Victory of Islam'
As the start of the referendum nears, security is tight, with tens of thousands of police and troops deployed to keep order.
President Morsi has also given the army the power to arrest civilians, raising fears that Egypt is moving back towards military rule.
The increased security presence has not stopped clashes flaring between the rival camps in the northern port city of Alexandria.
Dozens fought with clubs, stones and other weapons. A number of cars were set alight and several people were injured.
The violence reportedly broke out after a cleric at a mosque had urged worshippers to vote "Yes".
One pro-constitution rally in Cairo has already drawn 2,000 people, with more gatherings on both sides expected during the day.
Sheik Mohammed Sayyed, who is linked to Mr Morsi's Muslim Brotherhood, said during Friday prayers at a mosque in Assuit: "Tomorrow is the day we will seek victory of Islam."
But the April 6 opposition group said in its online campaign against the draft document: "It's you who will pay the price if you vote 'yes'. 'No' to the constitution."
A new Egyptian constitution is seen as a major milestone following the revolution that ousted Mubarak in 2011.
The BBC's Jon Leyne in Cairo says the referendum is not just a vote on a few obscure clauses.
He says it is about the future direction of Egypt - whether it should be an Islamic country or a secular one, a country with its own distinctive Middle Eastern identity or a country more in tune with Western and European values.
The vote on the draft - a densely written document passed by an 85-member constituent assembly composed of mostly Islamists earlier this month - has sharpened the polarisation between liberal groups and the powerful Muslim Brotherhood.
Critics say the wording of the draft would give a green light to Islamic clerics having a say over legislation and civil liberties.
Polls will open at 08:00 (06:00 GMT) on Saturday in Cairo, Alexandria and eight other provinces. The other half of the country will vote a week later.
Polling had to be spread out because so few judges were willing to supervise the vote.
Mohamed ElBaradei, a Nobel Peace Prize winner who heads the National Salvation Front, wrote on his Twitter feed: "Insistence on referendum in an explosive, polarised, chaotic and lawless environment is leading country to the brink."
Earlier this week, leading opposition figure Hamdeen Sabbahi said the Front would still call for a boycott if key conditions were not met by Saturday.
On Friday it was unclear if a boycott would be called.
Last weekend, President Morsi offered a concession to the opposition by annulling a 22 November decree that gave him sweeping new powers.