ALEXANDRIA, Egypt (Reuters) - Police fired teargas on Friday when supporters of President Mohamed Mursi and his opponents hurled stones at each other in Egypt's second city on the eve of a vote on a new constitution shaped by Islamists, a Reuters witness said.

Dozens of opponents of the new constitution and thousands of Islamists, separated by several lines of riot police, hurled rocks over the security cordon at each other near a mosque in Alexandria that was the focus for violence last week.

"God is great," Islamists chanted when the stone-throwing began.