If passed, the amendments would extend the president's term in office from five to seven years. A new first vice president would be installed and the president would get the power to call snap elections and easily dissolve the parliament.

Opposition groups staged protests ahead of the polls, denouncing them as President Aliyev's plan to increase his family's influence in the country. The former Soviet republic has vast oil resources.

The Council of Europe also criticized the draft modifications, saying their implementation "would severely upset the balance of power by giving unprecedented powers of the president." According to Amnesty International, the amendments would lead to violations of individual freedom. "The referendum has been accompanied by arrests and intimidation... Those who have attempted to criticize and campaign against these proposals have faced assaults and harassment by the authorities," Amnesty said in a statement.

President Ilham Aliyev, 54, has led his country since his father, Heydar Aliyev's death in 2003.  He won a landslide victory in polls in 2013, with OSCE observers pointing out several problems with the vote.  The next elections are in 2018 and President Aliyev is expected to contest yet again after a 2009 referendum scrapped the limit of two terms for a candidate.

Azerbaijan, located between Iran and Russia is a secular country with a predominantly Shiite Muslim population. It has tried to position itself as a modern European state, hosting the Formula One Races earlier this year and the Eurovision Song Contest in 2014.

Activists have however raised concerns about the country's human rights record, with watchdog Freedom House saying, "President Ilham Aliyev is the person most responsible for Azerbaijan's appalling human rights recordof the last decade."

mg/rg (AFP, AP)