Sri Lanka's acting president and prime minister, Ranil Wickremesinghe, has asked the speaker of parliament to nominate a new prime minister, his media team said after President Gotabaya Rajapaksa fled the country.
"Acting President and Prime Minister Ranil Wickremesinghe has informed Speaker Mahinda Yapa Abeywardena to nominate a prime minister who is acceptable to both the government and opposition," the team said in a statement.
Protesters, angered by a severe economic crisis, have sought the ousting of both Mr Rajapaksa and Mr Wickremesinghe.
Earlier, Sri Lankan troops stood with their weapons lowered in the grounds of the prime minister's office, doing nothing to halt the huge mass of people wandering through the compound, despite orders to "restore order".
Some of the civilians sang or waved the Sri Lankan flag, with its motif of a golden lion brandishing a sword, after they lobbed back tear gas canisters and pushed past elite commandos to occupy the premises in the capital Colombo.
Thousands of people cheered as they breached the walls of the colonial-era compound on a leafy boulevard, opening yet another symbol of state power to the public.
The office was the fourth government building occupied by protesters in as many days, following the seizure of the president's seafront office and the official residences of Sri Lanka's two most senior elected officials.
And as with those earlier conquests, by evening the compound had been repurposed into a public attraction, with demonstrators who helped storm the building hours earlier now chaperoning others through its rooms.
"We feel proud," said Satish Bee, a businessman who came to explore the compound once the dust had settled.
"There's no proper governance in this country. It has never been good... The youngsters, they don't want to continue like this."
Guards abandoned a losing battle to halt the crowd's advance less than two hours after the building's usual occupant, prime minister Ranil Wickremesinghe, was declared Sri Lanka's acting head of state by incumbent Gotabaya Rajapaksa.
Mr Wickremesinghe declared a nationwide state of emergency and soon appeared on television to warn that troops had been instructed to do "what is necessary" to return the building to government control.
But on the ground, his words went unheeded.
People began mobbing the office in the morning, after news spread through the capital that Mr Rajapaksa - blamed by many for driving the country to economic ruin - had left the island nation on a military aircraft bound for the Maldives.
What followed was an object lesson in patience and strategy from a crowd hardened by earlier confrontations with security forces over months of protests.
Some carried red traffic cones to smother and safely extinguish tear gas rounds periodically fired into the street by guards stationed along the walls.
Others guided friends or strangers blinded by the smoke to safety behind the cover of a wall, helping to flush their eyes with fluid.
Bolder members of the crowd peeled off a part of the gate and sections of wrought iron fence, prompting fresh barrages of tear gas - and loud cheers when still-smouldering canisters were thrown back at the troops that fired them.
In his televised statement, Mr Wickremesinghe made allusions to "fascists" trying to "take over".
Dhaniz Ali, one of those walking through the compound after it was occupied, said that protesters would continue to find new government buildings to occupy.
"We are not terrorists," he said. "We are just Sri Lankan citizens here to save the country."
