Tunisian law professor Kais Saied speaks to the reporters and supporters Sunday, Oct. 13, 2019 in Tunis. Saied looked set to assume Tunisia's presidency after polling agencies suggested he overwhelmingly won Sunday's runoff election in the country that unleashed the Arab Spring pro-democracy uprisings. File photo: AP Photo/Mosa'ab Elshamy.

Tunis - Independent law professor Kais Saied has overwhelmingly won Tunisia's presidential run-off that was held Sunday as the North African country grapples with economic and security challenges, according to a polling agency.

Saied has secured 72.53% of the vote against 27.47% for media mogul Nabil Karoui, the polling firm Emrhod Consulting added, citing exit polls.

It has been less than a decade since Tunisia, the origin of the 2010-11 Arab Spring revolts, toppled its long-time autocratic government in favour of democratic elections.

Social unrest, militant attacks and an economic slowdown have afflicted the country on its fledgling democratic path. The unemployment rate is about 15%.

Saied, 61, declared his victory, calling it a "revolution within the constitutional legitimacy."

Speaking at a press conference in Tunis Sunday night, he pledged to honour Tunisia's international obligations.

"We are aware of the size of responsibility and realize what the state means," added Saied who has no political experience.

"Today, we are trying to build a new Tunisia," he said.

Thousands of Saied's backers celebrated his reported win in central Tunis.

The conservative academic appeals mainly to young Tunisians disenchanted with politicians whom they accuse of failing to improve their post-uprising lives.

The official result of the run-off is expected by Tuesday.

Video: Kim Kay/African News Agency

The turnout in Sunday's election stood at 57.8% after 70% of the ballot was counted, the electoral commission said at a press briefing.

About 7.2 million people were registered to vote in Sunday's 10-hour polling.

Saied has campaigned to fight corruption and support decentralization.

Karoui, 56, presents himself as an advocate of Tunisia's poor and marginalized as the head of the recently founded centre-left Party of Qalb Tounes (Heart of Tunisia).

Both had topped the election's first round on September 15, defeating contenders from mainstream political parties.

The two political outsiders' electioneering has been very unusual, with Karoui having been released only four days before the final round.

Saied has kept a low profile since the first round and later announcing that he would stop campaigning for "ethical reasons" related to the lack of equal opportunity between the two candidates.

The presidential election, originally scheduled for November, was pushed forward by the death of Tunisia's first democratically elected president, Beji Caid Essebsi, in July, five months before the end of his term.

Last week, Tunisia held its legislative elections, in which Karoui's party came second with 38 seats, while the moderate Islamist Ennahda movement has emerged as the strongest force with 52 seats in the 217-member parliament.

With no clear majority at the fractious parliament, Ennahda is expected to face a tough challenge in forming a new government.