Supporters and party officials from the All People’s Congress were sifting through polling data from the presidential vote when the military surrounded party headquarters.

DAKAR, Senegal — Senior officials from Sierra Leone’s main opposition party on Sunday accused the country’s military of shooting live ammunition and tear gas into their headquarters, raising tensions in the small West African nation a day after presidential elections.

Samura Kamara, the presidential candidate of the opposition All People’s Congress, had gathered his supporters, party staff and local officials at the headquarters in Freetown, the capital, to sift through data from Saturday’s vote when the military surrounded the building and fired at the crowds gathered outside, according to Mayor Yvonne Aki-Sawyerr of Freetown, who was inside the building.

“There was a festive mood, people were playing music and dancing outside,” Ms. Aki-Sawyerr said in a telephone interview after she had been evacuated from the building on Sunday evening, coughing from the tear gas.

A New York Times reporter at the scene saw a truck loaded with soldiers carrying semiautomatic weapons, and others holding tear-gas launchers. Reports of live ammunition being fired could not immediately confirmed.

Drone footage showed the building engulfed in smoke, with tear gas canisters thrown around it.

The Sierra Leonean police said in a statement on Sunday evening that supporters of the A.P.C. party had paraded through the streets of Freetown claiming to have won the elections, although results have yet to be officially announced.

“As the situation became unbearable, the police had to fire tear gas canisters so as to disperse the crowd, which was harassing people on the road,” the statement said.

Representatives from the government or the military could not be immediately reached for comment. A spokesman for the country’s national security agency denied that the military was present at the scene.

Sierra Leoneans went to the polls on Saturday to elect their next president amid a crippling economic crisis and widespread doubt that either of the two favorites — the incumbent, Julius Maada Bio, and Mr. Kamara — can heal the country’s ills.

Over the past year, inflation has reached its highest level in two decades. The national currency is one of Africa’s weakest. And Sierra Leone, one of the world’s poorest countries, has one of West Africa’s highest youth unemployment rates.

Mr. Bio, a former military leader who participated in two coups during the country’s civil war in the 1990s, was elected president in 2018, beating Mr. Kamara in a tight race. While Mr. Bio is considered the favorite in this year’s vote, a runoff is considered likely; candidates need 55 percent of the vote to secure a victory in the first round.

The unrest on Sunday came after violent protests over rising prices left more than two dozen people dead last summer, including police officers, which had raised fears of further tension ahead of the vote. On Wednesday, supporters of Mr. Kamara clashed with security forces in front of the party’s headquarters, but election observers said voting went without major disturbance on Saturday.

The Carter Center, which has observers monitoring the election, urged parties not to release data before the country’s electoral commission. In a statement on Sunday, it also expressed concerns over the lack of transparency in the vote tallying.

That afternoon, dozens of people were trapped inside the headquarters of the opposition party for more than an hour as they were about to celebrate provisional results in some of Freetown’s districts that appeared to favor Mr. Kamara.

Uncertain of what was happening outside, and whether soldiers had penetrated the building, Ms. Aki-Sawyerr said she and about 20 people crawled toward Mr. Kamara’s office to escape the tear gas.

Mr. Kamara said live rounds had been fired at his office’s door, and posted a photo of what appeared to be a bullet hole on social media.

One woman was severely wounded and appeared unresponsive, according to a Reuters reporter who was there. Ms. Aki-Sawyerr said the woman had been brought to Mr. Kamara’s office.

“I’m in shock,” she said. “I am sorry this is happening to my country.”