President Ilham Aliyev was re-elected in 2008
Voters in Azerbaijan have overwhelmingly approved proposals to lift the two-term limit for presidents, the election commission has announced.
More than 90% of those who voted in Wednesday's referendum backed the change to the constitution, it said.
President Ilham Aliyev, who had backed the amendment, will now be able to extend his presidency beyond 2013.
Opposition parties have complained of voting irregularities and say Mr Aliyev could now become president for life.
The chairman of Azerbaijan's Central Elections Commission, Mazahir Panahov, said that with almost all the ballots counted, 92% of voters had approved removing presidential term limits from the constitution.
It means President Aliyev, who was re-elected last October with nearly 89% of ballots cast, is free to run again whenever the next election is held.
The president - who succeeded his father, the late long-serving leader, Heydar Aliyev - is in his second and what would have been his final term in office.
The ruling New Azerbaijan Party, which supports the president and proposed the constitutional amendments, said the result would increase democracy for the oil-rich former Soviet state.
But members of the main opposition bloc argued it would allow Mr Aliyev to remain in power indefinitely.
The opposition had decided to boycott the vote in an attempt to deem the referendum null and void. During the day, activists also gathered evidence of what they said was ballot-stuffing.
But the BBC's Tom Esslemont in Baku says their campaign appears to have failed.
Official figures put turnout at more than 70%, far exceeding the figure needed to make the referendum legitimate. The opposition says turnout was below 25%.
Mr Aliyev's rule since 2003 has coincided with rapid economic growth in the Caucasus state fuelled by oil and gas pumped West from reserves in the Caspian Sea.
But the opposition and human-rights groups say Mr Aliyev's grip on power owes as much to strict curbs on democracy and media freedoms, and the personality cult built around his father, who died after a decade in power in 2003.
A series of other amendments, including new media restrictions that have been criticised by press freedom groups and local journalists, were also approved on Wednesday.
Azerbaijan's authorities say they are committed to international standards of democracy, but that they have an obligation to protect the country from forces they say are trying to sow instability.