NEW DELHI — Vernon Gonsalves, a rights activist, was preparing for his morning bath when the police banged on his front door. Officers rummaged through his home in Mumbai for nearly eight hours, confiscating books, his laptop, a hard drive and pen drives — and then arrested him.

“My dad’s phone was seized, and our phones were put on flight mode so people trying to contact us could not,” the activist’s son, Sagar Abraham-Gonsalves, said in an interview. “They did not ask us a lot of questions. They just kept raiding, pulling out books and academic works.”

Across India on Tuesday, from New Delhi to Hyderabad to Ranchi, police officers carried out similar raids on the homes of at least a half-dozen activists, writers and lawyers. All were known for supporting resistance movements and marginalized groups, or for speaking out against the government.

Five people, including Mr. Gonsalves, were taken into custody on suspicion of abetting communist groups, plotting the assassination of top government officials and inciting a large riot this year. Several other activists arrested in June have been accused of similar crimes.

The crackdown has prompted sharp responses from news media, government critics and public intellectuals, who called the charges a pretext for Prime Minister Narendra Modi’s government to punish dissenters. The news channel India Today broadcast a report headlined “Activists in Shackles,” questioning whether the week’s events constituted a “witch hunt.”

Major dailies published front-page articles and blistering editorials about the arrests. Writing in The Indian Express, Prashant Bhushan, an Indian lawyer, activist and opposition politician, drew a parallel to the 1970s, when Prime Minister Indira Gandhi suspended elections and curbed civil liberties for 21 months to tighten her grip on power.

“The arrests and raids are outrageous attempts to stifle voices of dissent and curb peaceful struggles against this government’s anti-people ideology,” Mr. Bhushan wrote. “Democracy is under siege in India.”

Writers noted that since Mr. Modi and his Hindu nationalist Bharatiya Janata Party ascended to power in 2014, a wave of nationalism driven by hard-line Hindu groups has spread, and several prominent critics of the party and the government have been killed.

The spark for the activists’ arrests can be traced to New Year’s Day, when thousands of low-caste Dalits, or “untouchables,” gathered at a monument in Bhima-Koregaon, a village near the city of Pune, to commemorate the victory 200 years ago of a British-led force against high-caste Hindus.

The 1818 battle is seen as a point of community pride for Dalits, who are at the bottom of India’s widely observed caste system and have long suffered from discrimination, despite the outlawing of “untouchability” decades ago.

After the ceremony started, a mob brandishing saffron flags, a political symbol representing Hinduism, attacked the Dalits, according to news reports, apparently objecting to the ceremony because it commemorated a battle won by British colonizers.

Rioters hurled stones, and at least one person was killed. The clashes spilled over into Mumbai, where crowds of people vandalized stores and temporarily shut down portions of the city.

Local police officials said they had traced the riot’s origins to a hard-line Hindu group. But with the arrest of the five activists this week, that attribution has shifted.

The police in Pune now say that at least some of the activists who were detained — Sudha Bharadwaj, Gautam Navlakha, Varavara Rao, Arun Ferreira and Mr. Gonsalves — incited the riots through speeches at an event for Dalit and leftist leaders before the January ceremony. But it is unclear which of the activists, if, any, attended the event, which played host to tens of thousands of people.

A few of the activists, whose résumés include helping workers to unionize, speaking out against rights abuses in Kashmir and supporting tribal populations displaced by mining projects, have been tried for crimes in the past.

Now they have been accused of being aligned with separatists in Kashmir and aiding India’s Maoist rebels, who are waging a longstanding war with the state in central India. Officers sifting through Mr. Gonsalves’s books were searching, in particular, for anything on Marx, Lenin or Mao.

According to news reports, a prosecutor in Pune on Wednesday called the activists communists who “possess Maoist materials,” were planning to assassinate top leaders in the government, had contacted arms dealers in Nepal and were recruiting college students for “their war against the nation.”

“These people have hatched a criminal conspiracy and waged war against the government of India,” the prosecutor, Ujjwala Pawar, was quoted as saying.

The activists have been charged under the Unlawful Activities Prevention Act, which authorizes raids and arrests without warrants if a person is suspected of supporting terrorism.

On Wednesday, several notable Indian intellectuals filed a petition in the country’s Supreme Court, demanding the activists’ release and alleging a “gross abuse of police power.”

The Supreme Court intervened, and called on the state government of Maharashtra to place the activists under house arrest until the matter is heard again in court. A three-judge panel of the court also issued a warning: “Dissent is the safety valve of democracy. If it is not allowed, the pressure cooker will burst.”

Vrinda Grover, a lawyer representing Ms. Bharadwaj, questioned the legality of the arrests, saying that police officials had refused to give her regular access to her client, despite direction from a court to do so.

“The police are clearly acting in contempt of a court order and with an impunity that is not normal,” she said. “The state has moved to the next level of criminalizing and demonizing people who are dissenting ideologically.”

K. Satyanarayana, a cultural studies professor whose house in Hyderabad was also searched, said he and his wife had endured a menacing interrogation by some 20 plainclothes police officers on Tuesday. They tore through his books on Dalit movements, he said, asked why he read Mao and Marx, confiscated lecture notes and manuscripts, and inquired how often his father-in-law, one of the activists arrested, had visited the couple’s home.

Then the police pressed further, Mr. Satyanarayana said, accosting the couple for hanging up photographs of Indian social reformers but not of Hindu gods and goddesses, and berating his wife, an upper-caste Brahmin, for not wearing red vermilion, a symbol of piety, on her forehead.

“They told my wife, ‘We understand that your husband is a Dalit and does not follow any religious practices, but you are a Brahmin,’ ” he said. “They were mocking us. They could have killed us.”