Zimbabweans have voted in a referendum on a new constitution that would limit future presidents to two terms.
Voters are expected to endorse the plans, which include devolution and a bill of rights.
Correspondents say many people do not understand the changes, and turnout at some polling stations was low.
President Robert Mugabe, who has led Zimbabwe since 1980, defended the vote and said the people had been widely consulted about the changes.
"We went round asking the people questions: what sort of parliament do you want? What sort of president do you want? And the people were giving their answer," he told the BBC.
"So, the people made the constitution."
Among other measures, the draft constitution proposes:
- A bill of rights to protect free expression
- Devolution to provincial authorities
- Scrapping the president's power to veto legislation
- Halting legal challenges against land redistribution
Mr Mugabe's Zanu-PF is in a shaky power-sharing deal with Prime Minister Morgan Tsvangirai's Movement for Democratic Change (MDC).
The two parties agreed to share power in 2008 to resolve a violent dispute over the result of Zimbabwe's last presidential election.
The draft constitution limits the president to two five-year terms, but will not apply retrospectively.
So 89-year-old Mr Mugabe will be able to stand for re-election in a poll expected in July.
Mr Tsvangirai, 61, who was defeated in the controversial 2008 election, is also expected to stand again.
"This is a new political dispensation, and I hope it sets in a new political culture. From the culture of impunity to a culture of constitutionalism," Mr Tsvangirai told reporters.
Campaigning for the referendum was marred by an attack on MDC activist Sten Zvorwadza, who was punched as he tried to put up posters on Friday.
The BBC's Andrew Harding witnessed the incident and said the youths also threw punches at him and his film crew.
Although no-one was seriously injured, the incident is a reminder of the violence lurking close to the surface in Zimbabwe, our correspondent says.
On Tuesday, a Zanu-PF official was injured when his house in north-eastern Zimbabwe was attacked with petrol bombs.
And in February, the 12-year-old son of an MDC activist died in an alleged arson attack in the eastern farming district of Headlands.
Polls opened at 05:00 GMT and closed at 17:00 GMT, and the voting day was largely peaceful.
Election officials said results of the referendum would be announced within five days.
During campaigning the MDC has focused on clauses guaranteeing protection against violence, and free and fair voting.
The Zanu-PF campaign highlighted the irreversibility of the land reform programme, which saw some 4,500 farms seized from mainly white commercial farmers.