A Zimbabwean election official counts ballot papers after the close of voting on a referendum in Harare on Saturday.

Norton, Zimbabwe - Zimbabweans look set to endorse a new constitution curbing the presidency, early results showed on Sunday, in a step toward elections to determine whether Robert Mugabe adds to three decades in power.

While the vote on the constitution, which will limit the number of times a president can serve, was largely free from violence, police raided an office of Mugabe arch-rival Prime Minister Morgan Tsvangirai and arrested five people.

Early results posted outside polling stations showed voters had overwhelmingly backed the new document as expected, although polls were marked by low turnout. Both Mugabe and Tsvangirai, rivals in the election expected in the second half of this year, had backed the new constitution.

After a violent and disputed vote in 2008, Mugabe was pushed into a power-sharing deal with Tsvangirai, who made the referendum a condition of that deal.

The new charter would set a maximum of two five-year terms for the president. 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 declaring emergency rule or dissolving parliament will need the approval of two-thirds of lawmakers, changes that will take effect after the next election.

Mugabe, who has led since independence in 1980 and is Africa's oldest leader at 89, has been accused of violence against opponents and undermining the cabinet and parliament.

While ordinary Zimbabweans appeared relieved by the peaceful vote, talk of elections was mixed with concern about a possible return to violence that has marred polls since 2000.

“This is a big step I tell you but we now need to clean our dirty and violent politics,” said Edgar Tazivei in the affluent Twinlakes suburb.

More than two million people voted, compared to six million eligible, said electoral official Rita Makarau. Results were being verified and officials have five days to announce them.

Local radio said most people voted in favour of the draft constitution. Results at one polling station near Norton, 48km west of Harare, showed 91 percent of voters backed the charter. - Reuters