Police officials declined to give an exact figure but said tens of thousands had converged on the area.
The hastily organised march was called Wednesday morning by Hazare who has been fasting in Delhi’s Tihar jail since being arrested by police the day before.
Hazare was detained as he prepared to begin an indefinite hunger strike in a Delhi public park to protest against what he sees as a watered-down anti-corruption law recently introduced in parliament.
The size of the rally caught police by surprise and significantly raised the stakes in Hazare’s stand-off with the government.
Only hours before, Prime Minister Manmohan Singh had condemned the activist’s hunger-strike as *”totally misconceived”* and a dangerous challenge to India’s parliamentary democracy.
The marchers who poured in from all over the city included everyone from school students still in uniform, to office workers who left their desks and retired people.
*”For once we have brought the issue of corruption to every street of India,”* said K.C. Malhotra, 68, a former history professor from Delhi University.
*”I am happy that Indians are united for a cause that will change our lives forever,”* he said.
*”We have to defeat corruption to stop it from eating up the system,”* said Govind Kumar, who joined the rally after spending the previous night demonstrating outside Tihar jail.
*”This is the battleground for us to fight,”* Kumar said.
Smaller protests were held in cities across India on Wednesday, including the financial capital Mumbai and the southern port of Chennai.
Hazare’s campaign has tapped into a deep reservoir of national discontent in India over the corruption that permeates every level of society, from petty functionaries to top officials.
It has also piled the pressure on Singh’s government which has been hit by a series of high-profile graft scandals involving some senior ministers.