Tear gas fired at protesters outside the prime minister’s office.

COLOMBO, Sri Lanka — Police and military forces used tear gas to try to disperse a growing crowd outside the office of Sri Lanka’s prime minister, who was the top leader in the country after the president fled.

Protesters tried to push through the gates of the office of the prime minister, Ranil Wickremesinghe. A military helicopter flew overhead. Some people entered the grounds. Protesters have also demanded that Mr. Wickremesinghe resign. A spokesman for Mr. Wickremesinghe said the prime minister was not in his office.

Mr. Wickremesinghe expects to be sworn in as acting president, according to the Constitution, once President Gotabaya Rajapaksa hands in his resignation.

Mr. Rajapaksa fled to the Maldives on Wednesday morning. Parliament has yet to receive an official resignation letter.

Overnight, thousands of people arrived in Colombo to join the already huge group of protesters that helped overrun the presidential residence on Saturday.