Preliminary results show Erdogan losing majority in Turkey's fiercely fought elections

Neither Turkey's President Recep Tayyip Erdogan nor his main rival looked to have secured the 50% of votes to win the elections, preliminary election results showed, raising the prospects of a runoff vote.

State-run Anadolu news agency reported projections based on 90.54% of the votes counted, showing Erdogan having 49.86% of votes, compared to 44.38% for the main opposition candidate, Kemal Kilicdaroglu.

The third candidate, Sinan Ogan, received 5.30% of votes, according to Anadolu, raising the possibility he could be a kingmaker in a runoff. He tweeted that a second vote is "quite possible," and that "Turkish nationalists and Ataturkists are in a key position for this election."

Sunday's race poses the biggest challenge yet to Turkey's strongman leader. He faces economic headwinds and criticism that the impact of the devastating February 6 earthquake was made worse by lax building controls and a shambolic rescue effort.

Ballots of the 64 million eligible to vote were still being counted six hours after polling stations closed across the country.

For the first time, Turkey's factious opposition has coalesced around a single candidate, Kilicdaroglu, who represents an election coalition of six opposition parties.

Earlier on Sunday, Ankara Mayor Mansur Yavas, who is the vice-presidential candidate for the main opposition Nation Alliance bloc, contested Anadolu's results, saying the agency is unreliable. He added that the opposition's data showed Kilicdaroglu as being ahead of Erdogan.

Erdogan took to Twitter to ask his supporters "to stay at the ballot boxes, no matter what until the results are officially finalized."

"While the election was held in such a positive and democratic atmosphere and the vote counting is still going on, trying to announce results hastily means usurpation of the national will," tweeted Erdogan.

Can Selcuki, managing director of Istanbul Research Center told CNN's Becky Anderson that a runoff is likely.

"I think this is going to be a neck-to-neck race," he said. "Very highly likely to be not ending in the first round - that's what it seems to be."

A candidate must win over 50% of the vote on Sunday night in order to be elected. Otherwise Turkey will head to a run-off on May 28.

Speaking to CNN from a polling station in Istanbul's Beyogly district, voter Korhan Futaci, 46, said: "My vote is for freedom. My vote is for the future of our kids. I'm hopeful."

Yeliz Sahin, 46, whose brother and his son died in the earthquake, said: "It's a historical moment that we've been waiting for for 20 years. This whole system needs to change."

Meanwhile first-time voter Eren Uzmele, 19, said: "The future of the country is in our hands. It's in the hands of the youth."

Kilicdaroglu, a mild mannered 74-year-old former bureaucrat, has promised to fix Turkey's faltering economy and restore democratic institutions compromised by a slide to authoritarianism during Erdogan's tenure.

After casting his vote in Istanbul, Erdogan told reporters: "We pray to God for a better future for our country, our nation, and Turkish democracy. It is very important for all of our voters to cast their votes until 17.00 in the evening without any worries for demonstrating the strength of Turkish democracy."

Meanwhile, after voting in Ankara, Kilicdaroglu said: "We all missed democracy, being together and embracing so much. Hopefully, from now on you will see spring will come to this country and it will always continue."

Erdogan concluded his election campaign on Saturday night by praying at Hagia Sophia - a mosque and major historic site in Istanbul. In contrast, Kilicdaroglu visited the tomb of Mustafa Kemal Ataturk, the founder of modern Turkey and staunch secularist.

Erdogan has been extolling the virtues of his long rule, campaigning on a platform of stability, independent foreign policy and continuing to bolster Turkey's defense industry. Recently, he raised the wages of government workers by 45% and lowered the retirement age.

Over the last two years, Turkey's currency has plummeted and prices have ballooned, prompting a cost of living crisis that has chipped away at Erdogan's conservative, working class support base.

When a vicious earthquake on February 6 laid waste to large parts of southeast Turkey, Erdogan's battled political aftershocks. His critics chastized him for a botched rescue effort and lax building controls that his ruling Justice and Development (AK) party presided over for two decades.

In the weeks after the quake, the government rounded up dozens of contractors, construction inspectors and project managers for violating building rules. Critics dismissed the move as scapegoating.

The government has also apologized for "mistakes" that were made in the immediate aftermath of the disaster.

The quake claimed over 51,000 lives in Turkey and neighboring Syrian. Thousands are still unaccounted for, with unmarked graves peppering the southeastern Turkish countryside.

On Thursday, Kilicdaroglu was boosted further by the late withdrawal from the race of a minor candidate, Muharrem Ince. Ince had low polling numbers but some opposition figures feared he would split the anti-Erdogan vote.

Turkey holds elections every five years. More than 1.8 million voters living abroad already cast their votes on April 17, Turkish newspaper Daily Sabah reported Wednesday, citing the country's deputy foreign minister. Over 65 million Turks are eligible to vote.

The Supreme Election Council (YSK) chief Ahmet Yener said last month that at least 1 million voters in quake-stricken zones are expected not to vote this year amid displacement.