Zimbabweans have begun voting in a referendum over a new constitution.

The referendum is expected to be passed.

The reforms highlighted in the constitution would clip presidential powers and lead to an election that will decide whether Robert Mugabe extends his three-decade rule.

Mr Mugabe's ZANU-PF party and the Movement for Democratic Change (MDC) of his rival Prime Minister Morgan Tsvangirai are supporting the draft charter.

The support from both sides makes the vote almost a rubber stamp exercise.

Polling stations opened shortly after 5am Irish time.

In Mbare, the oldest township in the capital that has witnessed clashes between ZANU-PF and MDC supporters in the past, more than 100 people filed patiently into a polling station.

Results are expected within five days.

A new constitution is a prerequisite for the next presidential and parliamentary elections.

These elections are expected later this year under a power-sharing deal signed by Mr Mugabe and Mr Tsvangirai in 2008 after violent and disputed elections.

The run-up to the referendum has so far been peaceful.

The vote is seen as a dry run for the general elections later this year, where ZANU-PF is expected to face a stiff challenge from the MDC, although there are no reliable polls.