April 16, 2017 - 3:03pm
Voting is under way in Turkey in a landmark referendum that will determine whether President Recep Tayyip Erdogan will be granted sweeping new powers.
Mr Erdogan is seeking to replace Turkey's parliamentary system with an executive presidency.
Supporters say the move would streamline and modernise the country, but opponents fear it could lead to greater authoritarianism.
A "Yes" vote could also see Mr Erdogan remain in office until 2029.
About 55 million people are eligible to vote across 167,000 polling stations, with the results expected to be announced late on Sunday evening.
Polls suggest a narrow lead for "Yes".
How significant are the changes?
They would represent the most sweeping programme of constitutional changes since Turkey became a republic almost a century ago.
Mr Erdogan would be given vastly enhanced powers to appoint cabinet ministers, issue decrees, choose senior judges and dissolve parliament.
The new system would scrap the role of prime minister and concentrate power in the hands of the president, placing all state bureaucracy under his control.
Mr Erdogan says the changes are needed to address the security challenges faced by Turkey nine months after an attempted coup, and to avoid the fragile coalition governments of the past.
He says the new system will resemble those in France and the US and will bring calm in a time of turmoil marked by a Kurdish insurgency, Islamist militancy and conflict in neighbouring Syria that has led to a huge refugee influx.
Speaking at one of his final rallies in Istanbul's Tuzla district, Mr Erdogan told supporters that the new constitution would "bring stability and trust that is needed for our country to develop and grow".
"Turkey can leap into the future," he said.