Thousands of demonstrators flooded the streets of Kenya’s capital, Nairobi, and some broke into Parliament and briefly set fire to the entrance on Tuesday, after lawmakers approved tax increases that critics said would drive up the cost of living for millions.

During the protests, the police fired tear gas and guns, plunging the capital into turmoil. At least five people were fatally shot and 31 others injured, according to Amnesty International and several prominent Kenyan civic organizations. The toll could not be immediately confirmed. The independent Kenya Human Rights Commission posted a video that showed police officers firing as protesters marched toward them.

As tear gas wafted through the streets, some protesters climbed through the windows of Parliament after lawmakers voted 195 to 106 in favor of the tax bill on Tuesday, with supporters saying it would raise revenue for education and other essential services.

Kenya’s president, William Ruto, said he was deploying the military to crack down on what he called “treasonous events.” In a televised address on Tuesday night, Mr. Ruto said the debate about the tax bill had been “hijacked by dangerous people who have caused us the kind of loss we have incurred as a nation today.”

He vowed to punish those he said were responsible. “It is not in order or even conceivable that criminals pretending to be peaceful protesters can reign terror against the people, their elected representatives and the institutions established under our Constitution and expect to go scot-free,” Mr. Ruto added.

The defense minister, Aden Duale, said the defense forces had been deployed to support the police, who he said were responding to the “security emergency” caused by the protests, which spread to other Kenyan cities.

The turmoil over the finance bill has shaken Kenya, an East African economic powerhouse of 54 million people that has long been an anchor of stability in a tumultuous region. Last week, at least one person was killed and 200 others injured in protests across the country, according to Amnesty International.

Mr. Ruto’s government introduced the finance bill in May. The majority leader in Parliament, Kimani Ichung’wah, has said the bill is “crucial” to secure revenue for important government initiatives, including the construction of roads, the hiring of teachers and the funding of fertilizer subsidies for farmers.

Supporters also say the additional taxes will limit borrowing for a country facing a heavy debt burden.

“Without the passage of this bill, essential government operations would come to a standstill,” he wrote on social media last week, adding that lawmakers had responded to criticism by removing unpopular taxes on bread and other items.

But many Kenyans roundly criticized the legislation, saying it still added punitive taxes on imported staples like eggs, onions and cooking oil, and raised taxes on a wide range of goods and services. Detractors also pointed to corruption and mismanagement of state funds, and faulted the opulent lifestyle and extravagant spending that they said had characterized the administration of Mr. Ruto, who has been in office since 2022.

The president now has two weeks to sign the legislation or send it back to Parliament for amendments.

Young Kenyans who have helped to fuel the protests said that their movement transcends class, tribe and race.

Some protesters have confronted officials at public gatherings and in houses of worship, and carried coffins to the offices of lawmakers who supported the legislation.

“The politicians have for too long underestimated our power, energy and passion,” said Muchiri Mike, a 25-year-old content creator. “We are now asking questions and demanding answers, and they are surprised by this revolution happening at their doorsteps.”

On Saturday, nightclubs across Kenya played the national anthem to rally against the finance bill, and on Sunday, church leaders and congregants voiced their opposition to the tax increases at religious services.

As the protests spread on Tuesday, demonstrators draped themselves in Kenyan flags, blew whistles and plastic trumpets, and chanted, “Ruto must go.” In Nakuru, about 100 miles northwest of Nairobi, they blocked streets with burning tires and shouted, “Reject,” a reference to a hashtag that has galvanized the anti-tax movement on social media.

Government officials have blamed unspecified foreign powers for stirring up the protests and dismissed the demonstrators as privileged youngsters who wield iPhones, arrive at demonstrations via Uber and then go eat at KFC.

Protesters rejected that description.

“It’s not about how we get to the protests, but why we are here in the streets,” said Anita Barasa, 19, whose TikTok videos about the demonstrations have gained a large following. “They are trying to take attention away from our demands, but we, the cool kids, are seeing that we don’t have a bright future and want change.”

Before the demonstration on Tuesday, several activists who are prominent critics of the bill were abducted, according to the Law Society of Kenya. The abductors’ identities were not publicly known, but some were believed to be intelligence officers, according to the Law Society’s president, Faith Odhiambo. Ms. Odhiambo later said that some of those abducted had been released.

Several protesters said they had received threats or intimidating phone calls in the days and hours leading up to the protests and were fearing for their lives.

Rights groups have long accused successive Kenyan governments of kidnapping critics and torturing them. The police did not respond to a request for comment on Tuesday, but Kenya’s chief justice, Martha Koome, condemned the abductions, calling them “a direct assault” on the rule of law.

In a joint statement, the ambassadors of 13 Western embassies in Kenya, including the United States, said they were “shocked” by the scenes outside the Kenyan Parliament and “deeply concerned” by allegations that some protesters had been abducted by security forces.

“We condemn the violence reported during protests in Nairobi and around Kenya,” Matthew Miller, a U.S. State Department spokesman, said at a news conference in Washington on Tuesday. He added, “We urge restraint to restore order and provide space for dialogue.”

The half sister of former President Barack Obama, Auma Obama, was among the protesters engulfed in tear gas on Tuesday, according to CNN footage. “Young Kenyans are demonstrating for their rights,” Ms. Obama told a CNN reporter, before she began coughing and wincing.

“I can’t even see anymore,” she said.

Just after 6 p.m. in Nairobi, activists urged protesters to leave the city center. Public transportation services were not readily available, two protesters said, so they were walking home with others.

“Go home. While it’s still safe,” Boniface Mwangi, a Kenyan photographer and activist, wrote on social media. “The government will send goons to destroy, loot and blame peaceful protesters. They must listen to us. Spread the word for people to start walking home in groups. We shall be back.”

Reporting was contributed by Lynsey Chutel, Cassandra Vinograd, Jeffrey Gettleman and Michael Levenson.