A vast and jubilant crowd cheered as Gandhian activist Anna Hazare walked out of jail in New Delhi on Friday to carry on a hunger strike in public, the latest act in a drama of popular fury over corruption that has put India's government in a bind.

Fumbling as support for the anti-corruption crusader surged across the country, the government first jailed Hazare on Tuesday, then ordered his release and finally - when he refused to leave - granted him permission to stage his fast for 15 days.

There was a deafening roar of celebration as Hazare emerged from Delhi's Tihar jail into a throng of fans undeterred by monsoon rains. Live TV images broadcast across the country showed people perched on electric poles and even traffic lights to catch a glimpse of him, and many chanted "Anna we are with you".

Just past the gates he addressed the crowd. Raising his hand, he shouted "Victory to Mother India" and "A fight for freedom has begun", before slowly winding his way in a truck decorated with flags through the crush of supporters.

Dressed in his trademark white cap, kurta and spectacles, the slight 74-year-old has evoked memories of the ascetic independence leader Mahatma Gandhi, who is revered as the father of the nation.

Hazare's initial demand for tougher legislation against corruption mushroomed to catch the imagination of millions of Indians, especially a new middle class angry at constant bribes, from getting a driving license to winning a university place.

"We have not seen this kind of thing in the last 60 years in India," said S K Sharma, 48, a company executive, outside the jail as he waited for Hazare. "If this carries on in this way for the next four days, you will see a new changed India."

A top Hazare aide said he would first go to a memorial to Gandhi and later travel to open grounds in central Delhi, where supporters were making final preparations for his fast.

A blundering official response has led the Congress party-led government to face one of the most serious protest movements in India since the 1970s, just the latest in a series of setbacks for Prime Minister Manmohan Singh's second term that have paralysed policy making and economic reforms.

One banner outside the jail read "Wake up Manmohan Singh."  Many critics say Hazare's arrest only inflamed passions and galvanised thousands.

A medical team was on standby to monitor Hazare's health as he began his hunger strike in jail. A sharp deterioration in his condition could further worsen the crisis for the government, although his supporters say it is not a fast-to-death.

A weak political opposition means that the government should still survive the crisis, but it could further dim the prospect for economic reforms and hurt the Congress party in key state polls in 2012 that will pave the way for a general election in 2014.

The protests across cities in India, fanned by social networks, have not only rocked the ruling Congress party, they have sent shockwaves through the political class as a whole.

Hazare is not some out-of-the-blue phenonemen, however. Underlying change has been underway for years in India as its once-statist economy globalises, bolstered by a widely used freedom of information act, aggressive private media and the election of state politicians who have rejected traditional caste-support bases to win on governance issues.

"Anna Hazare is just a catalyst who happens to chime with the middle class mood today," wrote commentator Swagato Ganguly in The Times of India.

Students, lawyers, teachers, executives and civil servants have taken to streets in cities and remote villages stretching to the southern end of the country.

In the financial capital, Mumbai, the city's iconic lunch carriers, known as Dabbawallas, were reportedly set to go on strike in sympathy with Hazare. -Reuters