Video footage from inside the building showed hundreds of protesters packing into rooms and corridors, while hundreds also milled around the grounds outside.
A Sri Lankan court on Friday named former president Maithripala Sirisena as a suspect in the 2019 Easter bombings in which 270 people, including 11 Indians, were killed.
Sri Lankan police on Saturday fired tear gas and water cannons to disperse anti-government protestors here as the ongoing agitation demanding the resignation of President Gotabaya Rajapaksa over the worst economic crisis intensified as it entered its 50th day.
Wickremesinghe will resign after an all-party government is established and the majority is secured in Parliament.
Sri Lankan security forces raided the main anti-government protest camp at the President's Secretariat in Colombo early on Friday, arresting nine people and injuring several others, as the protesters continued to occupy the sensitive area despite the resignation of Gotabaya Rajapaksa as president.
The President had been moved out of his residence on Friday, in anticipation of Saturday's protests.
Xi Jinping is winning the war without firing a shot in Sri Lanka, observes Colonel R Hariharan (retd).
A woman suicide bomber blew herself up inside the Colombo Fort railway station in the heart of Colombo, hours after a grenade explosion inside the Dehiwala Zoo near Colombo left seven people including two children injured.