Sri Lanka's President Gotabaya Rajapaksa submitted his resignation on Thursday shortly after reaching Singapore, the parliamentary speaker's office announced, days after the head of state fled protests triggered by his country's worst-ever economic crisis.

Rajapaksa resigned by email, Indunil Yapa, the speaker's spokesperson said hours after he landed in Singapore following the protesters' storming of his palace over the weekend.

The resigned President fled to the Maldives on Wednesday and left there for Singapore a day later. 

"The authenticity and the legality of the e-mail will have to be checked out" before being formally accepted, Yapa told AFP, adding a formal announcement was expected on Friday. 

Rajapaksa would be the first president to resign since Sri Lanka adopted a presidential system of government in 1978.

Under Sri Lanka's constitution, Prime Minister Ranil Wickremesinghe -- whose resignation is also being demanded by protesters -- would automatically become acting president until parliament can appoint a successor.

The Sri Lankan parliament will hold a presidential election on July 20 and appoint a caretaker government, which will remain in power until the next general election.

Rajapaksa, his wife Ioma, and their two bodyguards arrived in Singapore from Male on board a Saudia airline flight.

Singapore's Foreign Ministry confirmed that Rajapaksa had been allowed to enter the country for a "private visit", adding that "He has not asked for asylum and neither has he been granted any asylum."

According to Sri Lankan security forces, Rajapaksa is expected to look to stay in Singapore for some time, before potentially moving to the United Arab Emirates.

Protesters hand back official buildings

In Colombo, demonstrators left several of the emblematic state buildings they had overrun in recent days after Wickremesinghe instructed security forces to restore order and declared a state of emergency.

"We are peacefully withdrawing from the Presidential Palace, the Presidential Secretariat and the Prime Minister's Office with immediate effect, but will continue our struggle," a spokesperson for the protesters said.

Police said a soldier and a constable were injured in overnight clashes with protesters outside the national parliament as security forces failed an attempt to storm the legislature.

The main hospital in Colombo said that about 85 people were admitted with injuries on Wednesday, with one man suffocating to death after being tear-gassed at the premier's office.

The military and the police were issued with orders Thursday to firmly put down any violence and warned troublemakers they were "legitimately empowered to exercise their force."

Sri Lanka defaulted on its $51-billion foreign debt

Rajapaksa is accused of mismanaging the economy to a point where the country has run out of foreign exchange to finance even the most essential imports, leading to severe hardships for its 22 million people, with four out of five Sri Lankans skipping meals.

Sri Lanka defaulted on its $51-billion foreign debt in April and is in talks with the IMF for a possible bailout.

The island has nearly exhausted its already scarce supplies of petrol with the government ordering the closure of non-essential offices and schools to reduce commuting and save fuel.

Diplomatic sources said Rajapaksa's attempts to secure a visa to the United States had been turned down because he had renounced his US citizenship in 2019 before running for president.