Turkey’s President Recep Tayyip Erdogan has claimed victory in critical elections, securing an executive presidency with sweeping powers.

Speaking in televised remarks from Istanbul, the 64-year-old said “the nation has entrusted to me the responsibility of the presidency and the executive duty”.

He also declared victory for the People’s Alliance, an electoral cooperation between his ruling Justice and Development Party and the small Nationalist Movement Party, saying they had a “parliamentary majority” in the 600-member assembly.

Sunday’s elections are putting into force a stronger presidential system, allowing the president to form the government, appoint ministers, vice presidents and top bureaucrats, issue decrees, prepare the budget and impose states of emergency.

Turkey Elections
Muharrem Ince, presidential candidate of Turkey’s main opposition Republican People’s Party (Emrah Gurel/AP)

The leading Turkish opposition party said it believes the results for the presidential elections are incomplete and may go to a second round.

Spokesman Bulent Tezcan of the Republican People’s Party criticised Turkey’s state-run news agency for reporting that Mr Erdogan has won enough to avoid a run-off and accused the agency of distorting the results.

He said “there is a high probability the presidential election will go to a second round”.

The state-run Anadolu news agency has Mr Erdogan leading the race with 52.63%, more than the 50% required to avoid a second round on July 8.

Mr Erdogan’s ruling Justice and Development Party, or AKP, was also hoping to retain its majority in parliament.

But Mr Erdogan — who has been in power since 2003 — faced a more robust and united opposition, which vowed to return Turkey to a parliamentary democracy with strong checks and balances.

Five candidates ran against Mr Erdogan in the presidential race.

Mr Erdogan’s main challenger was 54-year-old former physics teacher Muharrem Ince, who was backed by the centre-left main opposition Republican People’s Party, or CHP, and wooed crowds with an unexpectedly engaging election campaign.

His rallies in Turkey’s three main cities of Istanbul, Ankara and Izmir drew massive numbers.

Turkey was also electing 600 politicians to parliament — 50 more than in the previous assembly.