Sri Lanka's ruling SLPP party on Friday decided to back interim president Ranil Wickremesinghe in the parliamentary vote to be held next week to elect the successor to Gotabaya Rajapaksa, who resigned after unprecedented protests against his government.

Sri Lanka Podujana Peramuna (SLPP) General Secretary Sagara Kariyawasam said that their support would be extended to Prime Minister Wickremesinghe, who was on Friday sworn in as the interim president until Parliament elects a successor to Rajapaksa.

The party decided to support 73-year-old Wickremesinghe, who was once its arch rival, despite the SLPP breakaway Dullas Alahapperuma declaring his candidacy. The former information minister became the first to announce candidature at the vote which is to take place on July 20.

Alahapperuma said he was expecting cross-party support as an apolitical candidate in the presidential race to fill the void for the balance term of the "disgraced" Rajapaksa.

Rajapaksa agreed to step down after thousands of protesters stormed his official residence, blaming him for the unprecedented economic crisis that has brought the country to its knees.

He, however, fled to the Maldives without resigning from his office. From the Maldives, he went to Singapore on Thursday from where he sent in his resignation.

Alahapperuma was among the group of 10 SLPP MPs who declared independence from the ruling coalition as the political crisis triggered by the economic crisis came to the fore.

Wickremesinghe has just his seat in the 225-member assembly hence would be solely dependent on support from the SLPP.

The main Opposition SJB leader Sajith Premadasa is yet to announce his candidacy. He has the support of 50 plus MPs.

Sri Lanka, a country of 22 million people, is under the grip of an unprecedented economic turmoil, the worst in seven decades, leaving millions struggling to buy food, medicine, fuel and other essentials.