ISTANBUL (AP) — The first polling stations have opened in Turkey's historic referendum on reforms that would concentrate power in the hands of the nation's president.

The 18 constitutional changes would convert Turkey's system of government from parliamentary to presidential, and abolish the office of the prime minister.

President Recep Tayyip Erdogan, who called the referendum and has championed the "yes" campaign, says the proposed "Turkish style" presidential system will ensure the country no longer risks having weak governments. Opponents fear the change will lead to autocratic one-man rule, ensuring Erdogan, who has been accused of repressing rights and freedoms, could govern until 2029 with few checks and balances.

Polls in the east opened at 7 a.m. (0400 GMT), while those in the west are to open an hour later.