More than 55 million Turkish citizens began voting across the country on sunday, in a historic referendum proposing key constitutional changes, including giving wide-ranging executive powers to the president. Citizens are casting their ballots at 167,000 polling stations nationwide. Over 1 million of them are first-time voters who recently turned 18. Sunday's ballots have two sides with two different colors, and voters will indicate their choice by voting either "yes" on the white side of the paper or "no" on the brown side. Voters will impress a stamp on the side they have chosen. Voters will then place the ballot inside a yellow envelope that has the symbol of the Turkish Republic's supreme election board on it and cast their ballots. Voting is taking place between 7 a.m. and 4 p.m. in Turkey's eastern provinces. For the rest of the country, ballot boxes opened at 8 a.m. and people would be allowed to vote until 5 p.m. The electorate in Turkey is being asked to vote "yes" or "no" to an 18-article reform bill, which would also change the current parliamentary system to a presidential one. The "yes" campaign is backed by the ruling justice and development party and the opposition, nationalist movement party, whereas the main opposition, republican people's party, is in favor of "no". The constitutional changes have been discussed since president recep tayyip erdogan was voted president in august 2014. This marked the first time a Turkish president had been directly chosen by popular vote. The 18-article bill was passed by parliament in january, with 339 votes in favor - nine more than needed to put the proposal to a referendum. The reforms would extend the president's executive powers and the president would also be allowed to retain ties to a political party. The other major changes include lowering the age to become a lawmaker to 18 from 25, increasing the number of seats in parliament from 550 to 600, closing down military courts, and same-day parliamentary and presidential elections every five years. Simultaneous parliamentary and presidential elections for a five-year term would be held in november 2019 under the new constitution. Approximately 2.9 million Turkish expatriates have already voted in the referendum between March 27 and April 9. This referendum is their fourth trip to the polls since expatriates were permitted to vote in Turkish elections while overseas.