India's Supreme Court yesterday ordered five left-wing activists to be taken out of police custody and kept under house arrest amid widespread condemnation of their detention.

Police detained the five on Tuesday alleging links to banned left-wing Maoist militants.

Lawyers for the activists immediately took the case to the Supreme Court which gave Indian authorities until 6 September to respond to the challenge.

Opposition parties and civil rights groups have accused the government of seeking to silence critics.

And one Supreme Court justice, D Y Chandrachud, said: "Dissent is the safety valve of democracy, the pressure cooker will burst if you don't allow the safety valves."

The arrests follow months of tensions between right wing nationalist groups and advocates of free speech that has played out in college campuses and spilled over into the streets.

Critics also say several top journalists have been forced out of their jobs for their critical reporting of the government.

The five -- communist poet Varavara Rao, human rights lawyer Vernon Gonsalves, writer and lawyer Arun Ferreira, journalist and activist Gautam Navlakha, and trade unionist Sudha Bharadwaj -- are all established activists some of whom have been detained in the past.

Sudha Bharadwaj, who has been fighting for the rights of workers in parts of India such as Chhattisgarh where left-wing guerrilla groups operate, said the action against her was part of a broader crackdown on opponents of the government.

"The effort is whatever is the opposition to this regime, whether  it is workers rights, tribal rights, everybody who in the opposition is being rounded up," she told reporters outside her home in Faridabad, a short distance from  New Delhi.

The homes of other activists and lawyers were raided as part of the investigation. Five other people were detained in June.

Police have been investigating violence between low-caste Dalits and upper-caste groups following a political meeting near Pune on December 31 last year.

The Press Trust of India news agency quoted police as saying the five detained Tuesday had links to the meeting.

It also quoted security officials as saying that "two letters, purportedly exchanged by Maoist leaders indicating plans to assassinate Prime Minister Narendra Modi, BJP president Amit Shah and Home Minister Rajnath Singh, led to the police action."

The government did not immediately comment on the case. But Congress leader Gandhi led critics of Modi, whose right-wing Bharatiya Janata Party will seek re-election next year, accusing the government of seeking to silence its opponents.

"There is only place for one NGO in India and it's called the RSS," Gandhi said on Twitter, referring to the BJP's ideological Hindu nationalist backer, the Rashtriya Swayamsevak Sangh.

"Shut down all other NGOs. Jail all activists and shoot those that complain. Welcome to the new India."

Booker-prize winning author Arundhati Roy, an outspoken critic of Modi, said the arrests were an attempt to muzzle freedoms ahead of next year's polls.

"We cannot allow this to happen. We have to all come together. Otherwise we will lose every freedom that we cherish," she said, according to the Scroll news portal.

The Indian sections of Amnesty International and Oxfam released a joint statement calling the sweep "disturbing" and questioning whether the five had been detained for their rights work.

The latest wave of raids is "the second of such crackdowns on rights activists, advocates and journalists who have been critical of the state," said Aakar Patel, executive director of Amnesty International India.

"All these people have a history of working to protect the rights of some of India's most poor and marginalised people."

In July, Reporters Without Borders warned of deteriorating press freedom in the world's largest democracy amid a sharp rise in online hate campaigns directed at critics of Modi's Hindu nationalist government.

"It is sad that the government is arresting people who have been working on human rights," Prashant Bhushan, one of India's most prominent lawyers and activists told journalists after yesterday's court hearing.

"The court asked that they be kept under house arrest until the government submit their responses for the next hearing," Bhushan added.

A small demonstration was staged in central New Delhi ahead of yesterday's hearing.

"We are here today because we are fighting against the fascist and imperialist policies of this government," Aparna, president of the left-wing Indian Federation of Trade Unions told AFP.