Sri Lankan protesters refused to budge from President Gotabaya Rajapaksa's residence on Sunday, a day after they stormed his home, forcing him to flee with the navy and announce he would resign.

"Our struggle is not over," student leader Lahiru Weerasekara told reporters the day after Rajapaksa, currently taking refuge on a vessel offshore, said he would step down on Wednesday.

"We won't give up this struggle until he actually leaves."

The dramatic events on Saturday were the culmination of months of protests by people enraged by the South Asian island nation's unprecedented economic crisis and the Rajapaksa clan's incompetence and corruption.

Hundreds of thousands massed in Colombo demanding Rajapaksa take responsibility for shortages of medicines, food and fuel that have brought the once-relatively rich economy to its knees and caused misery for ordinary people.

After storming the gates of the colonial-era presidential palace, protesters lounged in its opulent rooms, somersaulting into the compound's pool and rummaging through Rajapaksa's clothes.

At a clock tower near the palace, activists hung an effigy of Rajapaksa on Sunday evening as thousands of onlookers cheered.

The streets leading to the palace were choked with people, some carrying toddlers and wheeling along the elderly.

Troops had fired in the air to help Rajapaksa escape on Saturday. The president then boarded a naval craft which steamed to the safety of the island's southern waters.

On Sunday the presidential palace was a free-for-all, with children and parents plonking on a grand piano, admiring the expensive artwork, picnicking and taking it in turns to sit in the president's chair.

"When leaders live in such luxury, they have no idea how the commoners manage," Buddhist monk Sri Sumeda told AFP. 

"This shows what can be done when people decide to exercise their power."

Rajapaksa's nearby seafront office was also overrun on Saturday, and Prime Minister Ranil Wickremesinghe's residence was set on fire even after he too offered to resign. 

Police said they arrested three men in connection with the arson attack at the premier's home.

- Resignation -
From the naval ship, 73-year-old Rajapaksa -- who had clung to power even after deadly nationwide violence in May forced his brother Mahinda Rajapaksa to quit as prime minister -- told the speaker of parliament he would step down on Wednesday.

Security forces on Saturday had attempted to disperse the huge crowds that mobbed Colombo's administrative district, triggering clashes. 

Colombo National Hospital said 105 people were brought in Saturday and that 55 remained under treatment on Sunday, including one in a "very critical" state with a gunshot wound.

After midnight Sri Lanka's top military officer, General Shavendra Silva, went on TV to appeal for calm and to "resolve the crisis situation peacefully and constitutionally".

A defence source said Rajapaksa, along with one of his brothers -- Basil -- was heading to a naval base in the northeast of the island. However, there was no official word their whereabouts.

Washington urged Sri Lankan leaders to act quickly to address the situation "with a commitment to the betterment of the nation -- not any one political party".

US Secretary of State Antony Blinken said on Sunday that Russia's restrictions on Ukrainian grain exports and the resulting rise in prices "may have contributed" to Sri Lanka's economic turmoil.

The European Union urged "all parties to cooperate and focus on a peaceful, democratic and orderly transition".

On Sunday it was unclear who, if anyone, would be able to garner enough support among lawmakers to succeed Rajapaksa.

"We are heading for dangerous uncertainty," minority Tamil legislator Dharmalingam Sithadthan told AFP. "Gota should have resigned immediately without leaving a power vacuum."

 - Default, desperation -
 The bankrupt government has defaulted on its $51 billion external debt and is seeking an International Monetary Fund bailout.

The IMF said Sunday that it hopes for "a resolution of the current situation that will allow for resumption of our dialogue".

Demonstrators had maintained a months-long protest camp outside Rajapaksa's office demanding his resignation. 

The camp was the scene of clashes in May when a gang of Rajapaksa loyalists attacked peaceful protesters. Nine people died.

- Cricket goes on -
The unrest comes at the tail end of Australia's cricket tour of Sri Lanka, with Pakistan's squad also on the island training for a series of matches beginning next Saturday. 

"Today obviously the country is in turmoil, (with) people outside having their say. We could obviously hear it, I mean we can still hear it now," Australian player Steve Smith said on Saturday.

Cricket officials said there were no plans to change the Australia and Pakistan schedules and that the sport was unaffected by the political turmoil.