Ankara, Turkey (CNN) Millions of Turks voted Sunday on a controversial new draft constitution that would give sweeping new powers to the country's president, Recep Tayyip Erdogan.

Voters were being asked to endorse an 18-article reform package put forward by the ruling Justice and Development Party that would replace the current system of parliamentary democracy with a powerful executive presidency.

Amid tight security, Erdogan cast his vote at a school near his home in Istanbul, surrounded by members of his family. He hoped Turks would make the "expected" choice, he said.

Polls closed at 5pm local time and results were expected later.

Turkish President Recep Tayyip Erdogan casts his vote accompanied by his wife Emine Erdogan at a polling station in the Uskudar district of Istanbul.

Earlier in the day, three people were reported to have died after an exchange of gunfire near a polling station in the southeastern province of Diyarbakır. The cause of the clash was not immediately clear and it was not known if there was a connection with the referendum.