Campaigning for Turkey's crucial referendum on whether to expand presidential powers has entered its final stretch, with President Recep Tayyip Erdogan addressing flag-waving supporters in an Istanbul neighborhood to drum up support for his "yes" campaign.

Erdogan has long championed the idea of changing Turkey's system of government from parliamentary to presidential. He is calling on his countrymen to vote on Sunday to approve constitutional changes that would abolish the office of the prime minister, handing all executive power to the president. The change, he says, will bring much-needed stability to Turkey.

But critics argue Erdogan, in power as prime minister or president since 2003, is becoming increasingly autocratic and fear the changes will simply cement his hold on power in a system that will have few checks and balances.