The measure -- which calls for a two-round popular vote to elect the president -- is part of a package of sweeping constitutional changes that still needs to be passed by parliament in its entirety before being sent to the president for approval.

The reforms are being rushed through parliament by the ruling Justice and Development Party (AKP) after it failed twice to get its presidential candidate, Foreign Minister Abdullah Gul, elected in parliamentary votes boycotted by the opposition.

The prospect of Gul, a former Islamist, becoming head of state sparked mass secular protests on the grounds that his election would increase the influence of Islam in all fields of life.

Opponents say the AKP, the moderate offshoot of a now-banned Islamist movement, is not truly committed to Turkey's secular system and harbours ambitions to erode the separation of state and religion.

In an initial televised vote on the amendment to elect the president by popular vote, 370 legislators in the 550-seat house voted in favour, while one voted against it.

The AKP has 351 seats in the house and has won pledges of support from a minor opposition party to secure the at least two-thirds majority -- or 367 votes -- needed for the package to be adopted without a referendum.