Turkish opposition Republican People's Party, CHP, members and others are currently gathering at polling stations for a primary election to endorse detained Istanbul Mayor Ekrem Imamoglu as candidate for the next presidential election.
The CHP urged non-party members to vote to boost public resistance amid Imamoglu's detention over charges including graft and aiding a terrorist group.
However, Imamoglu has repeatedly denied the charges.
CHP, which has over 1.5 million members, set up 5,600 ballot boxes for voting across all of Turkey's 81 provinces.
Polls are said to be closing at 1400 GMT.
The next election is reportedly scheduled to be held in 2028.
