Voting in a constitutional referendum in Azerbaijan began on Monday in a move which could increase presidents' tenures from five to seven years.
Among 23 proposed constitutional changes and six new articles are plans to also give the head of state the right to call early elections plus the lifting of a rule excluding presidential candidates under the age of 35.
If the changes are passed new leadership positions will be created including a "First Vice Presidency" and a number of deputy presidents. The new First Vice President position will also carry immunity from prosecution.
Some opponents say the changes would strengthen what they see as effectively a dynastic system of rule in the oil-rich Caspian Sea nation, which comes under frequent criticism from abroad for alleged human rights abuse and suppression of dissent. The Venice Commission, a European watchdog of constitutional law experts, last week said the measures would weaken political dissent.
Opposition groups staged mass protests ahead of the referendum, denouncing it as Aliyev's effort to extend his family's long grip on power in the oil-rich former Soviet republic.
Ilham Aliyev, 54, has led the country since his father Heydar, a former Soviet-era Politburo member, died after a decade in power in 2003.
Aliyev last won a landslide election victory in 2013 despite OSCE observers pointing to significant problems with the vote, with the next elections to be held in 2018. He can stand for an unlimited number of terms after a disputed referendum in 2009 scrapped the two-term limit on presidential mandates.
Azerbaijan's Central Election Committee released a statement Monday stating voting started at 8 a.m. local time (GMT 0400).
Over five million voters are registered to take part. Thirty-eight polling stations were set up for Azerbaijanis living abroad.
The referendum is being watched by 117 international observers; 53,300 local observers are also on duty. Voting will end at 5 p.m. local time (GMT 1300).
Azerbaijan, a majority-Muslim but secular country wedged between Iran and Russia on the Caspian Sea, has sought to position itself as a modern European state. It hosted the Eurovision Song Contest in 2012 and this year hosted its maiden Formula One race in Baku.