Turkey's presidential election is heading for a runoff on May 28, after none of the candidates, including incumbent President Recep Tayyip Erdogan, secured a majority in the first round.

Sunday's election was effectively a two-man race between Erdogan and his main rival Kemal Kilicdaroglu, who is the joint candidate of six opposition parties.

Preliminary results released by the election committee on Monday afternoon show Erdogan winning about 49.5 percent of votes, with Kilicdaroglu standing at nearly 44.9 percent.

Voter turnout, excluding ballots cast by voters living outside Turkey, was a very high 88.92 percent.

Erdogan vowed on Twitter to keep running without stop until the polling day and to fulfill his commitment to Turkish people.

Kilicdaroglu also expressed his determination to fight until the end in a video.

Erdogan has ruled the country for two decades as prime minister and president. Last year, he helped broker a deal that allowed Ukrainian farm products to be exported across the Black Sea. The exports had stopped due to Russia's invasion of Ukraine.

Kilicdaroglu is stressing that he will improve Turkey's relations with Western nations, which soured under Erdogan.