Sri Lanka's six-time prime minister Ranil Wickremesinghe was sworn in Thursday as president of the crisis-hit nation, with plans to form a unity government to manage the turmoil.

The 73-year-old veteran politician, who was overwhelmingly elected as head of state in a parliamentary vote Wednesday, took his oath of office with the country's police chief and top military brass standing behind him.

Official sources said the new leader was expected to shortly form a cabinet featuring several opposition lawmakers to steer the country out of its worst economic crisis since gaining independence from Britain.

Opposition leader Sajith Premadasa, who supported a rival candidate in Wednesday's vote, said he had met with Wickremesinghe to discuss how to protect the country from further "misery and disaster".

"We as an opposition will provide our constructive support for efforts to alleviate human suffering," Premadasa tweeted Thursday.

A foreign exchange crisis triggered by the coronavirus pandemic and exacerbated by mismanagement has left Sri Lanka suffering lengthy power blackouts and record-high inflation.

The country's 22 million people have also endured months of food, fuel and medicine shortages.

Public anger boiled over when tens of thousands of protesters stormed the home of then-president Gotabaya Rajapaksa, forcing him to step down.

Wickremesinghe has been tainted in the eyes of many Sri Lankans by his association with Rajapaksa, whose political party backed the new president's ascent.

"We don't need Ranil, he is the same as Gota," said Irfan Hussain, a poultry farmer in the capital Colombo.

"I don't think he is going to make our country better," he added. "He only thinks about himself, not the people."

Wickremesinghe is widely expected to invite his schoolmate and former public administration minister Dinesh Gunawardena to be the prime minister in the unity government.

But political sources said at least two other candidates were in the running.

"There will be a few MPs from the main opposition joining the cabinet," a source close to Wickremesinghe said, adding that he was keen to ensure a rainbow coalition.

Wickremesinghe prorogued parliament for 24 hours on Thursday to start a fresh session of the legislature, with chief government whip Prasanna Ranatunga telling reporters that the new president wanted to reconstitute parliamentary committees.

Live coverage of the ceremony to swear in Wickremesinghe at the tightly guarded parliament complex was cut off just as he and his wife Maithree walked into the building after reviewing a military parade.

A top defence official told AFP an investigation into why the broadcast was interrupted was underway.

Ranil Wickremesinghe, a former six-time prime minister, was sworn in as Sri Lanka's president on Thursday
Ranil Wickremesinghe, a former six-time prime minister, was sworn in as Sri Lanka's president on Thursday AFP / Arun SANKAR

A priority for the new government is to pursue ongoing bailout talks with the International Monetary Fund and restructure its unsustainable foreign debt.

The US Central Intelligence Agency overnight blamed Sri Lanka's financial crisis on high-debt Chinese investments, several of which funded white elephant infrastructure projects.

"The Chinese have a lot of weight to throw around and they can make a very appealing case for their investments," CIA chief Bill Burns said.

He said that Sri Lanka had "made some really dumb bets about their economic future", attributing the current "catastrophic" economic conditions to those decisions.

China is Sri Lanka's largest single bilateral foreign lender, accounting for more than 10 percent of its $51 billion external debt, on which the government announced a default in April.

A larger share of borrowings is owed to international sovereign bondholders, while economists have blamed unsustainable tax cuts pushed through by Rajapaksa for crippling government revenue.

Beijing's foreign ministry spokesman Weng Wenbin said comments from US officials would not affect China's "friendly and beneficial" relationship with Sri Lanka.

On Wednesday, Wickremesinghe vowed to take a tough line against those trying to disrupt his government.

He made a distinction between peaceful protesters and "troublemakers" engaging in illegal behaviour.

"If you try to topple the government, occupy the president's office and the prime minister's office, that is not democracy, it is against the law," Wickremesinghe said.

"We will deal with them firmly according to the law. We will not allow a minority of protesters to suppress the aspirations of the silent majority."

Protesters who stormed Rajapaksa's palace and toppled him earlier this month have accused Wickremesinghe of being a proxy of the former president's powerful family.

"I am not a friend of the Rajapaksas," he told reporters at the Gangaramaya temple. "I am a friend of the people."