The outcome is a strong vote of confidence for Prime Minister Recep Tayyip Erdogan's government, which the army-backed establishment suspects of seeking to undermine Turkey's fiercely-guarded secular system, analysts said.
The elections were called after political turmoil in April botched the AKP's bid to install a former Islamist as president. On Sunday, with 80 percent of the vote counted, the AKP was leading with 47.6 percent of the vote, according to nation-wide tallies by Turkish television. Final official results are expected next week.
Two surveys of results from sample ballot boxes across Turkey estimated that the AKP would eventually win more than 45 percent of the vote and enough parliamentary seats to once again form the government on its own. One of them, conducted for the NTV news channel, gave the AKP 45.6 percent and 332 seats in the 550-member parliament. The secularist main opposition Republican People's Party (CHP) finished second with 20 percent of votes and 104 seats, and the right-wing Nationalist Action Party (MHP) third with 14.4 percent and 85 seats, the survey showed.
No other party passed the 10-percent national threshold needed to enter parliament, but 29 independent candidates, mostly Kurds, would win seats, it said. "The result shows that the people do not blame political tensions on the AKP," political commentator Taha Akyol said. "The people have authorised the AKP to elect the next president."
The AKP, the offshoot of a now-banned Islamist movement, has disowned its radical past and describes itself as a conservative democrat party. It rejects accusations that it is not committed to the secular system. The issue came to a head in April when the AKP tried to install Foreign Minister Abdullah Gul as president, prompting a threat by the military to intervene. Millions of Turks took to the streets in mass demonstrations against the AKP as opposition parties blocked the parliamentary vote for president, forcing Erdogan to bring general elections forward from November. Erdogan's campaign focused on his government's impressive economic achievements since it swept to power five years ago.
His government has kept inflation in check while maintaining strong overall growth and attracting record foreign investment. It has also launched membership talks with the European Union. Erdogan, 53, casual in a blue shirt and dark trousers as he voted under the glare of cameras in Istanbul, said the elections would boost democracy. "Turkish democracy will emerge strengthened from these elections. This will be a message not just to our country but to the world," he said.
Voters in Ankara queued up at polling stations even before they opened, in part to catch the cooler hours of a sweltering day. Media reports said more than a quarter of Turkey's 42 million registered voters travelled across the country, cutting their vacations short to return to their electoral districts in time to cast their ballots. Participation was driven by widespread fears among secularists that the AKP has secret ambitions to erode the separation between state and religion. Voters applauded when the army chief, General Yasar Buyukanit, cast his vote at a polling station in Ankara. "It is a good thing you are there," shouted some people in the crowd.
The Turkish army, which usually tops opinion polls as the country's most trusted institution, has toppled four governments since 1960. If re-elected, Erdogan has promised to expand individual rights, introduce a new and more liberal constitution and tackle rampant unemployment.
Despite its expected victory, the AKP's current 352 members in the 550-seat parliament are likely to decrease because more parties will be represented. Analysts have warned that such a fragmented house could bring about a new confrontation over secularism when the freshly elected lawmakers settle down to their first task: electing the next head of state. Erdogan has said he will seek compromise in the presidential elections, but insists that the candidate must be from his party.