Dinesh Gunawardena sworn in as Sri Lanka's new PM

The event came just hours after security forces raided a protest camp on government grounds in the main city of Colombo and cleared part of it, with at least nine arrests, as the new administration moves to crack down on protesters.

A former minister from the Podujana Peramuna party, Gunawardena took the oath of office in the presence of Wickremesinghe, seated in front of uniformed military officers in a room packed with lawmakers and officials.

The rest of the cabinet is expected to be sworn in later on Friday.

Sri Lanka's crisis, the result of economic mismanagement and the fallout of conflict in Ukraine, sparked months of mass protests and eventually forced then president Gotabaya Rajapaksa to flee the country.

Wickremesinghe declared a state of emergency while seeking a bailout from the International Monetary Fund.

"A joint operation involving the military, police and police special forces was launched in the early hours to recover the presidential secretariat from the protesters as they have no legal right to hold it," police spokesperson Nalin Thalduwa told Reuters.

"Nine people, including two injured, have been arrested."

Angry at the pre-dawn raids, hundreds of protesters marched from the city's main railway station towards the Galle Face protest site, where they were held back by military and riot police manning barricades.

"The very first day he used the armed forces - this is the face of Ranil Wickremesinghe," said Rajeevkanth Rajkumar, CEO of a construction company and one of the protesters. "We don't want any more innocent people to be injured. But we will go to that place (the protest site) at any cost."

Opposition politician Anura Kumara Dissanayake, who lost the vote for the presidency, said on Twitter: "Let's bring down the brutal ... regime that viciously attacked the protesters at Galle Face".

Protest organisers said hundreds of security personnel surrounded the "Gota Go Gama" protest camp, mockingly named after Rajapaksa, after midnight and then took apart a section of it.

At least 50 protesters were injured, the organisers said, including some journalists who were beaten by security forces. Hospital sources said two were hospitalised.

"They beat us really cruelly," said Buddhika Abeyrathne, 34, a protester who witnessed the raid but did not appear injured himself. "Mr Wickremesinghe doesn’t know what democracy is."

'DESPICABLE'

Previous emergency regulations in the island nation of 22 million have been used to give powers to the military to detain and arrest protesters, and curtail the right to protest.

After surrounding the protest camp, security personnel moved in front of the presidential secretariat, started dismantling some tents and assaulted protesters, protest organiser Manjula Samarasekara said.

Security forces appeared to have taken control of the entire secretariat, with many more personnel visible inside the building perimeter that was earlier this month seized by protesters, along with the president and prime minister's official residences. The residences were later handed back to government authorities.

Protest organiser Chameera Dedduwage told Reuters they had planned to hand over the presidential secretariat to government authorities on Friday afternoon. Police said they had no information on that.

U.S. and British diplomats expressed concern over developments.

"We urge restraint by authorities and immediate access to medical attention for those injured," U.S. Ambassador to Sri Lanka, Julie Chung, said on Twitter.

The Bar Association of Sri Lanka said the crackdown could destabilise the country, which is in need of foreign aid and a bailout from the International Monetary Fund.