Tunisia's influential Islamist-inspired party Ennahdha said Friday it will support law professor and political outsider Kais Saied in a presidential runoff against jailed media magnate Nabil Karoui.

The latest twist in the electoral race came a day after the North African country's longtime dictator Zine El Abidine Ben Ali, who was ousted in 2011, died in exile in Saudi Arabia.

"Ennahdha has chosen to support the people's choice," the party's spokesman Imed Khemiri told AFP after last Sunday's first round of polling in which Saied finished ahead with 18.4% of the vote.

The surprise result of the election, contested by more than 20 candidates, thrust to the fore both Saied and Karoui, likewise from outside the world of traditional Tunisian politics.

Karoui came second with 15.6%, said the electoral commission ISIE, and Ennahdha, a key force in parliament, followed with 12.9% with its first-ever candidate to run for the presidency, Abdelfattah Mourou.

The result was a major upset for Tunisia's political establishment, in place since the fall of Ben Ali eight years ago after mass protests that sparked the Arab Spring revolts.

According to a lawyer claiming to be close to Ben Ali's family, the late president could be buried on Friday or Saturday in the Muslim holy city of Mecca, in western Saudi Arabia.

The funeral would be attended by family members residing in Saudi Arabia and other countries, said rapper K2Rhym, himself a son-in-law of Ben Ali living in the kingdom.

On the post-Ben Ali political front, Saied, a fiercely independent academic aged 61, advocates a radical decentralisation of power, with local democracy and the ability to remove elected officials from office during their mandates.

He is seen as strongly conservative on social issues, and has defended the death penalty, criminalisation of homosexuality and a sexual assault law that punishes unmarried couples who engage in public displays of affection.

Karoui, a 56-year-old media mogul, has been held in prison since August 23 under investigation for alleged money laundering.

He remains eligible to run as long as any conviction does not also specifically deprive him of his civil rights, according to ISIE.

Karoui has used his popular television channel Nessma to launch high-profile charity campaigns, often appearing in designer suits as he criss-crossed the country to meet with some of its poorest before his incarceration.