Gang rape on New Delhi bus sparks protests across India - video Reuters

Tens of thousands of demonstrators took to the streets across India on Wednesday, calling on authorities to stem the rising tide of violent sexual attacks on women, after a 23-year-old medical student was raped and beaten by six men on a Delhi bus.

The incident on Sunday night has convulsed India, sparking fierce criticism of the police, rows in parliament, blanket coverage in the media and even a debate on the role of revealing outfits worn by stars of Bollywood films.

Amitabh Bachchan, the country's biggest star, called on all Indians to become vigilantes.

"What is going wrong with our society, our people?" he asked in a Facebook post.

Sonia Gandhi, the president of the ruling Congress party, visited the victim in hospital where she is still in a critical condition after a series of emergency operations to treat serious injuries sustained in the attack.

In a letter to Sheila Dikshit, the chief minister of Delhi, Gandhi spoke of the "painful regularity" of such incidents and said it was "a shame that … our daughters, sisters, mothers are unsafe in the capital city".

Ministers have scrambled to shuffle blame elsewhere while senior police officers have promised tough action. Politicians have called for the imposition of the death penalty for rape.

So far four men – aged 25 to 33 – have been arrested. Two more are being sought. Several of the alleged attackers were living in a slum in the south of the capital. They include a bus driver, a fruitseller and a gym instructor.

The men are accused of attacking the woman and a male friend after the pair boarded a private, unlicensed bus on their way home from watching a film in south Delhi. The men, on what Indian newspapers have described as a "joyride", raped and tortured the woman and beat her friend with iron rods and other weapons, the police have said. They were stripped, robbed and dumped on the roadside near the city's main airport.

The incident is only the latest such attack. In one of the most infamous, a woman returning from work at a call centre in Gurgaon two years ago was raped by multiple attackers. The case has still to reach court. Newspapers frequently report incidents of abduction and rape as well as sexual harassment, known locally as "eve teasing".

The response of authorities – especially the police – is frequently to blame the victims.

Demonstrators in Delhi, a city of at least 15 million where there were 572 reported rapes last year – though the true total is believed to be much higher – said the harassment was getting worse.

"Every time I go out, I am hearing lewd remarks," said Asheeta Rudra, a 23-year-old student.

Shagufta Yasmin, 26, from the poor northern state of Bihar, said the problem was the same even when she went home.

"It's not just Delhi, even if it's bad here. It's everywhere," she said.

In one incident last year in the commercial capital, Mumbai, a 24-year-old man was stabbed to death after reprimanding men who were harassing a female friend.

"It is a huge social problem. Men are just taught to respect their elders, but not women," Jason Temasfieldt, the dead man's cousin, told the Guardian.

Temasfieldt, 25, now campaigns to raise awareness. "Sixty to 80 people stood by and watched my cousin being stabbed," he said. "They didn't intervene. If you try and stop harassment on a train or in the street then you are the one who people get angry at."

This summer, a TV crew filmed a 45-minute assault on a woman in a street in north-eastern India but made no attempt to intervene.

Much of the debate has focused on reinforcing legislation. However, many point out that the national conviction rate in rape cases brought to court is lower than 25%.

Others say deep discrimination is to blame. In many parts of India, female infants and foetuses have been routinely killed for decades, leading to a huge demographic imbalance and a shortage of sexual partners for young men. At the same time, education and economic change have meant new roles, aspirations and independence for many women.

"It's not about laws or enforcement. It's about a psyche, a mindset. That's what has to change," said Smita Sharma, a senior TV journalist.

Local gun campaigners have said that women should be able to defend themselves with firearms.

"The only effective deterrent is if women are armed and prepared to use the firearm in self-defence," said Abhijeet Singh, of Indians for Guns.