COLOMBO: Sri Lankan opposition leader Sajith Premadasa announced on Tuesday he had dropped out of the race to become president of the crisis-hit nation and promised his support to a rival candidate set to take on acting president Ranil Wickremesinghe.

Students and other groups planned a mass protest against Wickremesinghe's bid for president, as lawmakers gathered in parliament to finalise candidates for the role ahead of a vote on Wednesday. Protesters see Wickremesinghe as an ally of ousted president Gotabaya Rajapaksa.

"For the greater good of my country that I love and the people I cherish, I hereby withdraw my candidacy for the position of president," Premadasa said on Twitter.

He said his main opposition Samagi Jana Balawegaya party and "our alliance and our opposition partners will work hard towards making" Dullas Alahapperuma the winner.

Former journalist Alahapperuma, a ruling party lawmaker who has long operated in the shadows of the powerful Rajapaksa family that dominated the country's politics for decades, is seen as more acceptable to the protesters than Wickremesinghe. 

Six-time prime minister Wickremesinghe took over as acting president last week after a popular uprising against rocketing prices and shortages of food and fuel forced Rajapaksa to flee to Singapore and resign.

Another presidential contestant is Anura Kumara Dissanayaka, the leader of the left-wing Janatha Vimukti Peramuna party.

The next president will complete Rajapaksa's term that was scheduled to end in 2024.

Hit hard by the COVID-19 pandemic and tax cuts by the Rajapaksa government, Sri Lanka is in the midst of its worst economic crisis since it won independence from Britain in 1948.

Inflation of over 50% and shortages of food, fuel and medicines have brought thousands onto the streets in months of protests that culminated in Rajapaksa's ouster and forced the country to seek help from overseas.

India is willing to make more investments in Sri Lanka after supporting it with $3.8 billion this year, New Delhi's envoy in Colombo told the Indian Express newspaper.

"The idea is to respond to Sri Lanka's requests for enabling them to meet their foreign exchange crisis," said Gopal Baglay, India's high commissioner in Sri Lanka.

"We would like to continue to bring more investment into Sri Lanka because that will help create medium- and long-term capacity to respond within the Sri Lankan economy."

Sri Lanka has also sought assistance from its fourth-biggest lender, China.