Ousted president Hosni Mubarak is calling on Egyptians to approve the new constitution, his lawyer said late on Tuesday.

"This is the president's wish, in order to achieve our hope of building a new state," Fareed El-Deeb told the privately-owned Al-Mehwer TV channel.

Mubarak has twice requested permission to vote at the military hospital in Maadi where he is based, because he is too sick to vote at a polling station, he added.

The 85-year-old is on trial for his role in the killing of protesters during the January 2011 uprising that unseated him. He also faces charges of squandering public funds by selling natural gas to Israel at below market prices.

He was released from jail in August after a two year maximum detention provision lapsed.

Tuesday saw the first day of the constitution referendum. Voting will resume on Wednesday at 9am.

At least 9 were killed on Tuesday in nationwide clashes between Muslim Brotherhood members, local residents and security forces.

This constitution is the first electoral test in the roadmap put in place by the transitional authorities that replaced Mohamed Morsi after his ouster in July 2013.

According to the post-30 June political roadmap, a successful referendum will be followed by parliamentary and presidential elections within six months.