Supporters of Islamist President Mohamed Mursi and his opponents hurled rocks at each other in Egypt's second city of Alexandria on Friday.
The Islamists had gathered in support of an Islamic vision of Egypt's future laid out in a draft constitution that will be put to a referendum on Saturday.
Police fired tear gas as scores of opponents of the constitution and thousands of Islamists hurled rocks across a security cordon near a mosque that was the focus of violence last week.
Mursi and his Islamist allies back the draft constitution as a vital step in Egypt's transition to democracy almost two years after the fall of Hosni Mubarak.
The opposition says the draft, drawn up by an Islamist-dominated assembly, is a recipe for deepening divisions and more violence.
The vote had to be split over two days as a judges' boycott meant there were not enough legal observers for the whole country to vote together.
