The initial results had been expected to give Erdogan and his Islamist-rooted party a strong lead and it was expected to shorten as more votes are tallied across the nation of 81 million people.
But an AK Party official said the party expected Erdogan to win more than the required 50 percent to avoid a second round runoff. An unexpectedly strong showing by the AK Party's alliance partner, the nationalist MHP, could also mean Erdogan securing the parliamentary majority he seeks to govern freely.
Sunday's vote ushers in a powerful new executive presidency long sought by Erdogan and backed by a small majority of Turks in a 2017 referendum. Critics say it will further erode democracy in the NATO member state and entrench one-man rule.
With 70 percent of votes counted in the presidential race, Erdogan had 55 percent, ahead of his closest rival, Muharrem Ince, of the main opposition, secularist Republican People's Party (CHP), on 29 percent, broadcasters said.