CHITUNGWIZA, Zimbabwe - Zimbabweans voted on Saturday in a referendum expected to endorse a new constitution that would trim presidential powers and pave the way for an election to decide whether Robert Mugabe extends his three-decade rule.

Mugabe, Africa's oldest president at 89, has ruled the former British colony since independence in 1980 and has been accused of waging violent crackdowns on the opposition and weakening state institutions like the cabinet and parliament.

The new constitution would set a maximum two five-year terms for the president, starting with the next election, expected in the second half of this year. But the limit will not apply retroactively, so Mugabe could rule for another two terms.

Presidential decrees will also require majority backing in the cabinet, and declarations of emergency rule or dissolutions of parliament will need the approval of two-thirds of lawmakers, changes that will take effect after the next election.

Both Mugabe's ZANU-PF and the rival Movement for Democratic Change are backing the constitution, making Saturday's vote almost a rubber stamp exercise.

"We want peace in the country. Peace, peace, peace. It must begin with Robert Mugabe and go on to you and everyone else," said Mugabe as he voted in the Highfield township near downtown Harare, accompanied by his wife and daughter.

Polls around the country were set to close at 1700 GMT, and the Zimbabwe Electoral Commission (ZEC) said results of the referendum would be announced within five days. But some ZEC officials say the results could be in within 48 hours.

After a violent and disputed vote in 2008, Mugabe was pushed into a power-sharing agreement with arch-rival Morgan Tsvangirai, now prime minister.

Tsvangirai made the referendum on the new constitution a condition of the power-sharing deal and said there would be no point in holding new elections without it.

Turnout is expected to be low. A few people trickled into polling stations by mid-day, according to Reuters witnesses.

Tsvangirai voted in the town of Chitungwiza, some 30 km (20 miles) south of Harare.

"This is a new political dispensation and I hope it sets in a new political culture. From the culture of impunity to constitutionalism," Tsvangirai told journalists.

Focus on elections

Hundreds of voters filed patiently into polling stations earlier in Kuwadzana and Mbare, the oldest township in the capital, which has witnessed clashes between ZANU-PF and MDC supporters in the past.

"It is a good constitution because now a president can rule for 10 years at the most," said Douglas Muchena, after voting at a polling station in Avondale, just outside central Harare.

The run-up to the referendum was peaceful. Analysts say they are more worried about presidential and parliamentary elections later this year, where ZANU-PF is expected to face a stiff challenge from the MDC, although there are no reliable polls.

The periods preceding previous elections since 2000 have been marred by violence, and the MDC says hundreds of its members have been killed at the hands of Mugabe's youth brigades and independent war veterans supporters.

Tsvangirai defeated Mugabe in March 2008 but not by enough votes to avoid a second round of voting.

The former trade union leader was forced to quit the run-off race after a campaign of violence by Mugabe's supporters, but regional leaders intervened to force the two rivals to form a coalition government.

Although fragile and at times acrimonious, the unity government has eased political tensions and helped stabilise an economy which shrank 40 percent between 2000 and 2010.

Mugabe wants to continue with his nationalist policies, like seizing white-owned commercial farms and taking majority shares in foreign-owned firms.

The MDC says if it wins it will revive a once-vibrant economy, attract foreign investment and reduce the 80 percent unemployment rate, one of the world's highest.

Reuters