Zimbabwe's Prime Minister Morgan Tsvangirai cast his vote in a one-day referendum Saturday on a new constitution that all main political parties have backed, urging supporters to accept the draft document that will curb presidential powers.

Tsvangirai, thronged by supporters at a junior high school south of Harare, said a "Yes" vote marked a new turning point and "and one of the most important historical steps" for the southern African nation. He said it paved the way for a new chapter of the rule of law.

His supporters who have been killed in political violence over the past decade "will rest in peace because this is the most important stage we have been fighting for," Tsvangirai said. "I hope everyone will exercise their vote as a preliminary step to free and fair elections."

The proposed constitution would include a bill of rights guaranteeing freedom of expression and a limit of two five-year terms in office for the president. The latter means President Robert Mugabe, now 89, has the chance to stay in office for another decade.

Full scale presidential and parliamentary elections are slated for around July to end a shaky coalition government formed by regional leaders after the last violent and disputed national polls in 2008.

Supporters of Zimbabwean President Robert Mugabe greet his arrival to cast his vote during the country's referendum in the capital Harare. (Tsvangirayi Mukwazhi/Associated Press)

Officials said polling was busy in populous districts after voting stations opened at 7:00 a.m. across the country. Small knots of voters turned out early in remote areas and less populated or wealthier suburbs.

The proposed constitution reduces the entrenched powers of Zimbabwe's president and includes a range of democratic reforms demanded by regional mediators in Zimbabwe's decade-long political and economic crisis.

The voting day was announced exactly a month ago, and critics say voters were not given enough time to study the constitutional proposals in detail. About 9,400 voting stations have been set up and 12 million ballot papers have been printed. Results are expected within five days.

But Abigail Punungwe, a young mother with a baby on her back in a line at one voting station in Harare, said she hadn't read the 170-page draft constitution "but everyone is saying we must vote for it."

Elections monitors say printed copies were woefully inadequate in the two main local languages. Many rural Zimbabweans don't speak or read English. Monitors also pointed to only 200 braille copies being produced for the country's 40,000 blind people.

But cash shortages and administrative setbacks aside, voters in lines over 200 metres long in Harare waited quietly to cast their ballots. Cumbersome voters' lists were not used. The nation has 6.6 million registered voters, but on Saturday all Zimbabweans over the age of 18 carrying a valid citizens' identification document can vote during more than 12 hours of polling.

Polling stations using indelible finger ink on the hands of those who have already voted will stay open later into the evening if voters are still in line at the closing time.

Munganyi Nyarai, a polling officer in the western Harare township of Mbare, said more young people voted early at her post than in usual elections. Voting was running quickly and smoothly but some people in the line were turned away because they had not regularized their citizenship status and were still classified as "alien" Zimbabwe residents. Voters were made to turn off mobile phones as a security precaution to stop them from taking photographs inside polling booths.

Elections marred by violence

Since Tsvangirai, 61, the former opposition leader, founded his Movement for Democratic Change party four previous elections have been marred by violence and alleged vote-rigging blamed mostly on the ZANU-PF party of longtime ruler Robert Mugabe.

The draft constitution reduces presidential powers to pass authoritarian decrees and paves the way for a National Peace and Reconciliation Commission on past violence and human rights violations.

It also strengthens the bill of rights to protect all Zimbabweans from "torture, cruel, inhumane and degrading treatment or punishment" that would be enforced by a new constitutional Court with powers above the main existing highest court of appeal, the Supreme Court.

In urging supporters to vote "Yes," Mugabe's party says the draft recognizes as irreversible the seizure of thousands of white-owned commercial farms which have since 2000 been handed over to blacks. Black empowerment programs and the taking of control of foreign-owned mines and businesses by locals would also be irreversible.

Mugabe's party says the draft honours black guerrilla fighters who ended colonial rule after a seven-year bush war with white-led troops of the former colony of Rhodesia, as Zimbabwe was known before independence in 1980.