Rival sides in Egypt's political crisis are staging rallies in Cairo a day before the first round of voting begins on a contentious draft constitution.

The National Salvation Front of opposition groups has organised demonstrations at the presidential palace and in Cairo's Tahrir Square on Friday, after deciding to call on followers to vote "no" in the referendum scheduled for December 15 and 22.

Al Jazeera's Rory Challands, reporting from Cairo, said the opposition fears the constitution "gives too much emphasis on Islamic law ... They would like to see more emphasis given on rights and freedoms". In particular, those planning to vote against the draft constitution want additional rights for workers and women.

Live Box 2011111713397233347

The Coalition of Islamist Forces is describing a vote in favour of the draft as "yes" for Islam and has staged its own rally at Nasr City in the capital following mid-day prayers.

Rallies were also held in other cities, and in Alexandria, Egypt's second city, those demonstraitons turned violent, resulting in clashes between the two sides.

Witnesses said that a number of people were injured as the fighting spread from a mosque where Friday prayers were held to main roads. Scuffles started near the mosque when opposition members handing out flyers clashed with Morsi supporters.

Witnesses said that some supporters of the draft constitution brandished swords, while the opposition hurled stones after the sermon. At least two cars also were set on fire.

'This is democracy'

Those who support the draft say the constitutent assembly that helped draft the constitution represents the people of Egypt. In Nasr City, the people "are essentially saying 'this is democracy'", said our correspondent.

Our correspondent also said a victory for the opposition would prove difficult as the more conservative segments of society "have the stronger mobilisation".

Voting has been taking place at Egyptian embassies abroad and Egyptians abroad are voting for a third day, with more than 500,000 people expected to cast their votes in 150 countries.

The draft constitution, approved by the constituent assembly last month, has become the focus of Egypt's worst political crisis since the June election of Mohamed Morsi, the president.

Rival mass rallies held by both supporters and opponents of Morsi have become almost a daily occurrence in Cairo.

Clashes between the two groups killed at least seven people and injured hundreds more last week.

The crisis has necessitated a ramping up of security around the presidential palace, which has been the focal point of anti-Morsi protests.

Source: Al Jazeera and agencies