The protest on Saturday by the "Cockroach" youth movement aimed to draw thousands of demonstrators against Chief Election Commissioner Gyanesh Kumar over a revision of voter lists that critics say favours Prime Minister Narendra Modi's Bharatiya Janata Party.
"Long live the revolution," chanted some of the young protesters in central Delhi chased by police, who dragged scores of others into buses to be taken away, even as more arrived, a Reuters witness said.
"This is violating the rights of the people and the country will not tolerate this anymore," Yogendra Solanki, one of those being pushed into a bus, told Reuters.
Police also detained 'Cockroach Janta Party' founder Abhijeet Dipke and senior leaders Saurav Das and Ashutosh Ranka as the aircraft bringing them to Delhi arrived from Mumbai, CJP said in a statement.
"I have come to be arrested, arrest me ... I am not afraid of you guys," Dipke told police officers who spoke to the trio on board the aircraft, television images showed.
"No, this is not an arrest," one police officer replied. "Please co-operate."
CJP condemned the "authoritarian detention" of its leaders, which it called a "pre-planned interception" aimed at crippling the leadership of Saturday's rally and demanded their immediate release.
Representatives of two digital media outlets said on X that police detained four of their reporters while covering the protest.
Some lawyers protesting outside the Supreme Court were also picked up, the president of its bar association posted on X.
There was no immediate comment from police on the detentions.
Elsewhere across the city of 20 million, 45 metro stations and markets were shut and mobile internet suspended in the central business district.
Police boarded buses to check for protesters after stopping them at points of entry into the city, with cars and other vehicles also subjected to checks, Reuters witnesses said.
Barricades and concrete blocks stopped traffic, while anti-riot vehicles mounted with tear gas guns were stationed on key routes, they said.
"Why is the prime minister so scared of the country's youth, the country's people?" Dipke had asked before leaving for Delhi.
"Why did you need to close all the railways, the metro, the internet has been closed, roads have been closed? ... this is nothing but fear," he told the ANI news agency in the financial capital of Mumbai.
The protesters aimed to gather at Jantar Mantar, a protest site designated by authorities in the heart of New Delhi, at 10am, but security curbs delayed their schedule.
The protest, which the CJP called an effort to "Save Democracy", is planned as the biggest of a series of demonstrations launched last week after the Indian Express newspaper said Kumar's deputies had queried and disagreed with him over list revisions that dropped about 130 million voters.
Opposition parties have long accused the government of trying to fix voter lists to its advantage and were quick to resurrect the allegations following the report.
