Sri Lankan protesters have vowed to continue their struggle for a complete change of the system by abolishing the presidency, as the popular uprising that ousted Gotabaya Rajapaksa as president marked the 100th day on Sunday.

The anti-government protest began on April 9 near the presidential office and has been continuing without a break. “We will continue our fight till we achieve our goal for a complete change of the system," Father Jeewantha Peiris, a leading activist of the movement, said.

“This is a freedom struggle. We managed to send home an authoritarian President through people’s power," Peiris said.

Rajapaksa, 73, who fled to the Maldives on Wednesday and then landed in Singapore on Thursday, formally resigned on Friday, capping off a chaotic 72 hours in the crisis-hit nation that saw protesters storm many iconic buildings, including the President and the Prime Minister's residences here.

Acting president Wickremesinghe appears to be their next target for the protesters and the campaign to oust him has already begun.

“On July 5, we issued an action plan. Foremost of that was removing Gotabaya and defeating Ranil Wickremesinghe and the Rajapaksa regime," he said.

“We press for the abolition of the presidency to make it a true realisation of our action plan," he said. “We do not fear the government," the protesters chanted in chorus.

After occupying the three most important administrative buildings in the capital, the protesters vacated three of them other than the presidential office.

The protest had seen violence since it began mid-April. Some elements with extremist political agendas have been blamed for arson attacks on the personal properties of Sri Lankan leaders.

Wickremesinghe's private house suffered an arson attack the same day when Rajapaksa fled the country. He is one of the four candidates who seek to succeed Rajapaksa in the vote in Parliament scheduled for July 20.

Wickremesinghe, who is also the prime minister, on Friday pledged to maintain law and order after he was sworn in as Sri Lanka's interim president.

He said that the armed forces have been given the powers and the freedom to deal with any acts of violence and sabotage. "I am one hundred per cent supportive of peaceful demonstrations. There is a difference between rioters and protesters," he had said.

Wickremesinghe said the true protesters would not resort to unleashing violence.