Millions of rupees in cash left behind by President Gotabaya Rajapaksa when he fled his official residence in the capital will be handed over to court on Monday, police said.

Protesters discovered 17.85 million rupees (about $50,000) in crisp new banknotes but turned it over to police following Saturday's storming of the Presidential palace.

"The cash was taken over by the police and will be produced in court today," a police spokesman said.

Official sources said a suitcase full of documents had also been left behind at the stately mansion.

Rajapaksa took up residence at the two-century-old building after he was driven out of his private home on March 31 when protesters tried to storm it.

The 73-year-old leader escaped through a back door under escort from naval personnel and was taken away by boat, heading to the northeast of the island, official sources told AFP.

His exact whereabouts were not known Monday morning, but Prime Minister Ranil Wickremesinghe said Rajapaksa had officially informed him of his intention to resign.

The 73-year-old Wickremesinghe will automatically become acting president in the event of Rajapaksa's resignation, but has himself announced his willingness to step down if consensus is reached on forming a unity government.

Rajapaksa had already told parliamentary Speaker Mahinda Abeywardana that he will quit on Wednesday to allow a "peaceful transition", hours after he was forced out of his official residence.

Protesters discovered 17.85 million rupees (about $50,000) in crisp new banknotes at President Gotabaya Rajapaksa's official residence in Colombo
Protesters discovered 17.85 million rupees (about $50,000) in crisp new banknotes at President Gotabaya Rajapaksa's official residence in Colombo AFP / Arun SANKAR

Tens of thousands of protesters captured Rajapaksa's sea-front office shortly after overrunning the palace on Saturday.

Protesters had been camping outside the Presidential Secretariat for over three months demanding his resignation over the country's unprecedented economic crisis.

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 the 22 million population.

Thousands of men and women on Monday continued to occupy the state buildings they had taken over at the weekend, vowing to remain until Rajapaksa steps down.

The roads leading to the palace were choked with tens of thousands of people on Sunday visiting the mansion that had previously been the country's most tightly-guarded building.

An effigy of Rajapaksa was hung on a clock tower near the palace.

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

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