Indonesia's main opposition won most votes at last month's legislative elections but did worse than expected, final results confirmed Friday, as negotiations to build coalitions heat up ahead of July's presidential polls.

The Indonesian Democratic Party of Struggle (PDI-P) won 18.95 percent of the vote, the election commission announced, in line with unofficial tallies released at the time of the April 9 vote.

The results, which were released just before a midnight deadline after an 11th-hour push to finish counting, also confirmed President Susilo Bambang Yudhoyono's corruption-mired Democratic Party saw its support halve to around 10 percent.

While the results put the PDI-P in first place, the party did considerably worse than surveys predicted before the vote, meaning their popular presidential candidate, Jakarta governor Joko Widodo, faces a tougher path to become head of state.

A party, or coalition of parties, needs 25 percent of the national vote or 20 percent of seats in the lower house of parliament to field a presidential candidate.

The results mean the PDI-P will likely have to form a larger-than-expected coalition to ensure enough support at the July election.

The election commission will announce the number of seats that each party won in the coming days.

Intense negotiations have been taking place in recent weeks to build coalitions.

The NasDem party, which won 6.7 percent of the vote, has already thrown its weight behind the PDI-P and the National Awakening Party, which won nine percent, also reportedly announced its support for Widodo's party Friday.

However Widodo is likely to want to join up with more parties to build a strong bloc to take on the men seen as his main rivals for the presidency, ex-general Prabowo Subianto and controversial tycoon Aburizal Bakrie, analysts say.

Subianto's Gerindra party won 11.81 percent of the vote while Bakrie's Golkar, which used to be the political vehicle of former dictator Suharto, won 14.75 percent, according to the final results.

The officials engaged in the mammoth task of counting votes from across the world's biggest archipelago nation almost did not finish by the midnight deadline, which is set down in law.

There were numerous allegations from parties of vote-buying and falsifying results across the country of 250 million people, and the disputes slowed down counting in many areas.

Unresolved disputes are taken to the Constitutional Court, and the National Awakening Party was one of several parties saying it planned to do so.

"We are searching for justice and to ensure a fair vote," said party secretary general Imam Nahrawi.