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 neighbourhood 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.

The "yes" side is hoping a stronger presidency will ward off events like last July's attempted military coup.

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.

Turkey Referendum

Supporters of the draft constitution hold a placard that reads 'Yes God willing' as they listen to Turkey's President Erdogan during a last referendum rally in Istanbul's Umraniye district on Saturday. (Emrah Gurel/Associated Press)

They fear the changes would undermine Turkey's democracy and threaten free speech, and say the sign of things to come is in the large number of arrests and firings of academics, journalists, civil servants and political opponents since the coup attempt. 

A win could allow Erdogan to retain power for 12 more years under the draft constitution promoted by the AKP (Justice and Development Party). The constitutional changes would go into effect after the 2019 presidential elections.

"The most recent polls put both of these sides neck-and-neck still. It has been like that throughout the campaign," said CBC's Nik Köksal, reporting from Istanbul.

Kemal Kilicdaroglu, leader of Turkey's main opposition party CHP (Republican People's Party), spoke to a rally in  in Polatli, near the capital Ankara, on Saturday.

TURKEY-REFERENDUM/PREVIEW

At a rally near Ankara on Saturday, Kemal Kilicdaroglu, leader of Turkey's main opposition party CHP (Republican People's Party), warned of a 'one-man regime' if the 'yes' side wins. (Murad Sezer/Reuters)

"If we love our country, if we love our flag, if we care about our children and our country's future, what will we say?" he asked to the sound of the crowd chanting "no."

Kilicdaroglu also asked, "[Do] we want a democratic parliamentary system or do we want a one-man regime?"

At a rally in Istanbul, Erdogan urged voters to support what he called a forward-thinking presidency.

"Those who praise the old times, solely think of protecting their seats and their interests," he said. "None of them have worries, projects or visions about our country's future."

With files from CBC's Nik Köksal and Reuters