Thousands of 'cockroach' protesters are set to return to the streets of Delhi on Friday, days after police prevented their last mass demonstration and two of their leaders were jailed.

The Cockroach Janta Party (CJP), a youth-led movement seeking electoral reforms, has called on supporters to gather at Central Park in Connaught Place, a busy commercial district.

The call follows the jailing of two CJP leaders for five days after they entered Jantar Mantar, a protest site recently declared off-limits by police.

What began as a campaign against alleged electoral fraud has since become a wider fight over the right to protest. Central Park is not an approved protest venue either.

On Thursday evening, Delhi police warned protesters to stay away from Connaught Place, saying orders restricting public gatherings were already in place and anyone breaking them could face legal action.

Authorities also said the venue Central Park, a leafy public space surrounded by Connaught Place's white colonial-era buildings, would be closed for two days for "administrative reasons". Police said they were willing to allow a small group to wave the national flag and sing the national anthem somewhere else.

But CJP founder Abhijeet Dipke has shown no sign of backing down. He has called the protest Lehra Do Tiranga, or Wave the Tricolour, as many Indians informally refer to the country's orange-white-green flag as Tiranga. Dipke has said he is prepared to risk arrest himself.

Whether his supporters can reach the park is another question. Police barricades and mass detentions kept many away from last Saturday's demonstration. This time, Dipke has urged those unable to reach Delhi to raise the Indian flag and protest wherever they are.

The CJP has come a long way from May, when the movement began with an insult. After India's chief justice likened some unemployed young people to cockroaches, Dipke embraced the label and turned it into an online protest movement.

By July, he and his supporters were filling the streets over examination paper leaks, in protests that forced India's education minister Dharmendra Pradhan to resign. Within months, the "cockroaches" had become one of the most visible expressions of youth anger at Prime Minister Narendra Modi's government.

Now they are taking on something bigger - India's elections.

At issue is a sweeping revision of electoral rolls, known as Special Intensive Revision (SIR), that critics say has removed more than 130 million names, putting legitimate voters at risk of losing their right to vote.

The CJP wants Chief Election Commissioner Gyanesh Kumar to resign, accusing the poll panel of favouring Modi's ruling Bharatiya Janata Party (BJP). Both the commission and the government deny the allegations.

Friday's march comes less than a week after police prevented the movement's last mass demonstration from taking place, detaining its leaders and deploying officers across the capital before protesters could assemble.

Dipke and two senior organisers, Saurav Das and Ashutosh Ranka, were detained from within the aircraft upon landing in Delhi.

The capital was put under a sweeping security lockdown. Tens of thousands of police and paramilitary personnel had fanned out across Delhi, sealing roads, shutting metro stations and intercepting protesters long before they could reach Jantar Mantar, where the CJP had planned its mass demonstration.

The BBC witnessed dozens of people being detained, including journalists and students. In footage from across Delhi, protesters could be seen shouting as police seized them by the arms, dragged them across the pavement and pushed them into waiting buses.

Those who managed to gather elsewhere were swiftly dispersed. There were also reports of protesters being assaulted by police.

The BBC captured footage of a policeman slapping a detained protester inside a bus. The Delhi police did not respond to questions about the use of violence against protesters.

The scale of the crackdown drew widespread outrage, with the CJP likening the police action to India's Emergency, when civil liberties were suspended between 1975 and 1977.

Delhi police defended the measures as necessary to maintain public order and prevent unauthorised gatherings.

Dipke, Das and Ranka were released on Sunday after agreeing to maintain peace and good behaviour.

Police then took Jantar Mantar off Delhi's list of approved protest sites, telling demonstrators to go instead to Ramlila Maidan, Burari Ground or CBD Ground.

But Jantar Mantar is no ordinary patch of ground. Built in the 18th Century to study the stars, the observatory sits near parliament and has long been one of India's most recognisable stages for public dissent.

The CJP accused the authorities of pushing protesters away from the seat of power to make their demonstrations less visible and easier to ignore.

On Tuesday, Das and Ranka returned anyway, bringing a handful of supporters. They unfurled the Indian flag and shouted slogans against Kumar. Police said they had entered the restricted site without permission, some by climbing over a locked gate, and violated the conditions of their earlier release.

The following day, Das and Ranka were sent to jail for five days in judicial custody. Another organiser, Ajinkya Shinde, was released on a bond to maintain peace and good behaviour.

With two of its key organisers behind bars, the CJP heads into Friday's protest with its leadership depleted, though Dipke insists the march will go ahead and he does not intend to back down.

"I also may be jailed after this, but I am not worried. Tricolour is my pride and I will raise it," he said in a video message.

Police, meanwhile, are bracing themselves for another large gathering in the heart of Delhi. Senior officers met on Thursday to discuss security arrangements and possible traffic restrictions around Connaught Place.

The Delhi High Court also declined to block the protest after a local trader petitioned the court, warning that the gathering could disrupt traffic and business.

The CJP's campaign is unfolding alongside a separate wave of protests by India's opposition parties, which have also accused the Election Commission of manipulating voter rolls to benefit the BJP.

Last week, opposition leader Rahul Gandhi and other lawmakers attempted to march to the commission's headquarters in Delhi but were stopped by police and detained. Opposition politicians have since taken their grievances to President Droupadi Murmu and marched towards the Supreme Court.

Among those at Monday's march was Neha Bora, a feisty leader of the left-wing All India Students' Association (AISA), who has emerged as another prominent face of the demonstrations.

Detained while leading protesters last Saturday, she was later seen marching with Gandhi and his sister Priyanka Gandhi Vadra.

Although the CJP, student organisations and opposition parties have largely protested separately, their demands have increasingly converged. Gandhi has condemned the arrests of CJP organisers and called for Jantar Mantar to be reopened to peaceful demonstrators.

Home minister Amit Shah, meanwhile, has accused opposition parties of spreading falsehoods about the voter-verification exercise and defended the Election Commission's independence.