Erdogan, who has dominated Turkish politics for 14 years, has long pushed imbuing the presidency with greater political powers, arguing that strong leadership would help Turkey grow.

The main opposition party fears that if approved, the reforms would concentrate too much power in Erdogan's hands, turn the country into a de facto dictatorship and move Turkey away from democracy and its anchor in the West.

"They are trying to turn the democratic parliamentary regime into a totalitarian regime," said main opposition Republican Peoples' Party, or CHP, leader Kemal Kilicdaroglu.

Debate on the set of amendments is expected to last two weeks. The reforms must clear two rounds of balloting in parliament, known as the Grand National Assembly of Turkey, gaining at least 330 of the 550 votes.