The rallies to win the support of voters come a week ahead of the landmark referendum that will decide whether or not to adopt a presidential system of government in Turkey.
With only a week to go before voters in Turkey decide whether to change from a parliamentary to a presidential system of government, both the "Yes" and "No" camps are holding mass rallies on Saturday to drum up more support.
The "Yes" campaign being led by the ruling Justice and Development (AK) Party is holding its biggest rally so far in Istanbul's Yenikapi Square.
As many as one million people are expected to attend the rally which will be addressed by Turkish President Recep Tayyip Erdogan.
The upcoming referendum is a vote on a constitutional amendment package that if accepted, paves the way for a fully-fledged presidential system, while abolishing the position of the prime minister.
The proposed changes also include increasing the number of MPs from 550 to 600, and would lower the minimum age required to become an MP from 25 to 18.
Supporters of the "Yes" vote believe the proposed reforms will create a more efficient democracy in Turkey.
The "No" camp, spearheaded by Turkey's main opposition Republican People's Party (CHP), is organising its rally in Trabzon, in northeastern Turkey.
TRT World 's Anelise Borges reports from Istanbul's Yenikapi Square.