TUNIS: Tunisia's main Islamic party claimed Monday to have taken the biggest block of votes in historic free polls, as the cradle of the Arab Spring basked in praise for its democratic revolution.

Official results were not due until Tuesday, but provisional numbers released by media outlets appeared to confirm Ennahda's prediction that it would be the dominant force in Tunisia's constituent assembly.

The leader of the secular centre-left PDP party, tipped as Ennahda's main challenger before the vote, conceded defeat.

“The trend is clear. The PDP is badly placed. It is the decision of the Tunisian people. I bow before their choice,” leader Maya Jribi told AFP at her party's headquarters.

Instead, the leaders of two other leftist parties, Ettakatol and the Congress for the Republic (CPR), said they were fighting it out for second place, both expecting to get about 15 per cent.

Tunisians turned out en masse Sunday to elect an assembly seen as the custodian of the pro-democracy revolution that toppled longtime dictator Zine el Abidine Ben Ali nine months ago.

“We are not far from 40 per cent. It could be a bit more or a bit less, but we are sure to take 24 (of the 27) voting districts,” Samir Dilou, a member of Ennahda's political bureau told AFP, though another party member later put the figure at closer to 30 per cent.

Data posted on the site of independent radio station Mosaique FM gave Ennahda the lead based on non-definitive results from a few dozen polling centres.

The polls, for which over 90 percent of some 4.1 million registered voters turned out, won hearty acclaim from world leaders closely scrutinising developments on the soil of the Arab Spring's trailblazer.

“This landmark election constitutes a key step in the democratic transition of the country and a significant development in the overall democratic transformation in north Africa and the Middle East,” said UN chief Ban Ki-moon.

US President Barack Obama late Sunday hailed the vote as “an important step forward”.

The 27-member European Union vowed support for the new authorities, while former colonial power France hailed Tunisian voters' “democratic fervour”.

Ennahda sought to reassure investors and said it was open to a coalition with any party “without exception”.

“We would like to reassure our trade and economic partners, and all actors and investors, we hope very soon to have stability and the right conditions for investment in Tunisia,” executive party member Abdelhamid Jlassi told journalists in Tunis.

“The priorities for Tunisia are clear. They are stability, conditions for a dignified life and the building of democratic institutions in Tunisia. We are open to anyone who shares these objectives. We are open to all forces without exception,” he said.

The new assembly will be tasked with rewriting the constitution and appointing a president to form a caretaker government.

It will decide on the country's system of government and how to guarantee basic liberties, including women's rights, which many in Tunisia fear Ennahda would seek to diminish despite its assurances to the contrary.

It will also have interim authority to write laws and pass budgets.

Ennahda says it models itself on the ruling AKP party in Turkey, another Muslim-majority country which like Tunisia to date has a secular state.