Arundhati Roy's eagerly-awaited second novel went on sale Tuesday, two decades after her prize-winning debut "The God of Small Things" propelled her to global fame and launched her career as an outspoken critic of injustice in her native India.

Roy became the first Indian woman to win the prestigious Booker Prize with her 1997 work, which sold around eight million copies and turned the young author into a star of the literary world.

In the years that followed, she turned to non-fiction writing, taking on issues ranging from poverty and globalisation to the conflict in Kashmir in essays that were often highly critical of India's ruling class.

Her campaigning earned her the wrath of many in the Indian establishment and has clearly influenced her latest novel "The Ministry of Utmost Happiness", which she has said took 10 years to produce.

Publisher Penguin says it takes the reader "from the cramped neighbourhoods of Old Delhi into the burgeoning new metropolis" and on to the troubled Kashmir Valley and the jungles of central India, racked by a long-running Maoist rebellion.

"There was this huge sense of urgency when I was writing the political essays, each time you wanted to blow a space open, on any issue," Roy told The Hindu daily in an interview published last week.

"But fiction takes its time and is layered... It is not just a human rights report about how many people have been killed and where. How do you describe the psychosis of what is going on? Except through fiction."

Roy was praised at home when she became the first resident Indian to win the Booker for her novel about twins growing up in the southern state of Kerala. Previous Indian winners had lived outside the country.

The Times of India in an editorial entitled "Novel Indian" quoted a "prophecy" by James Joyce -- "The East shall wake the West awake/And ye shall have night for morn" -- which it said "seems to be coming true".

Roy recalled in a recent BBC interview how she was suddenly on the cover of every magazine -- until she spoke out against India's nuclear tests a year later.

"Not that I had a say in it, but I was being marketed as this new product of the global India," she said.

"And then suddenly the government did these nuclear tests... and I wrote this essay condemning the tests, and at that point the fairy princess was kicked off her pedestal in a minute."

- 'Scarring' -

Roy, now 55, went on to become one of India's most famous and polarising authors.

She was briefly jailed for contempt of court over her activism and still faces a sedition charge for challenging in 2010 India's right to rule the disputed Kashmir region.

She argues that India's economic boom has made a small minority rich on the sufferings of the poor, and has spent time researching the fight by Maoist rebels for land rights in the resource-rich jungles of central India.

Her criticism of the ruling Hindu nationalist Bharatiya Janata Party has been particularly fierce. She once called for Prime Minister Narendra Modi to be put on trial over the deadly anti-Muslim riots in the state of Gujarat in 2002, when he was chief minister.

Modi has been dogged by accusations he turned a blind eye to the violence, but a Supreme Court-ordered investigation in 2012 cleared him of any wrongdoing.

Internationally she remains a huge draw, lauded both for her activism and her writing, and the reviews of her second novel have been broadly -- though not universally -- positive.

The Financial Times said it was "as remarkable as her first" and  admirers would not be disappointed, while The New Yorker called it a "scarring novel of India's modern history".

But some critics were sceptical about her attempts to introduce political causes into her fiction.

"'Ministry' is two decades of polemic distilled into one book, with a superstructure of fiction to hold it together," said The Economist. "It does not work."

Roy attended a launch for the new novel on Monday evening in London at the start of a book tour that will also take her to the US.

Rajni Malhotra, owner of Bahrisons bookstore in New Delhi, said she expected sales to be good.

"She is a good novelist, you know," Malhotra told AFP. "She took 20 years to write this one, so everyone's expectations are very high and it's one of those hotly-anticipated books."