MUMBAI: Hundreds of people set out from Mumbai to India's capital, New Delhi, on Thursday in a caravan aimed at pressuring authorities to speed up trials of perpetrators of sex crimes, and to encourage victims to speak out.

Government data shows reported cases of overall crimes against women rose by 83 percent from 2007 to 2016, a year when four rape cases were reported every hour.

Campaigners say many sexual attacks remain unreported, as victims fear stigma or retribution.

Of the 35,000 rape cases reported to police in 2015, only 7,000 resulted in convictions, according to government data that showed a 40 percent increase in both numbers from three years earlier.

"I am here to seek a quick trial for my daughter. She has still not recovered," said Sohmat Singh Lodhi, whose four-year-old girl was raped in June by a man now awaiting trial.

"We just want him to be punished."

Organisers from the advocacy group Rashtriya Garima Abhiyan (National Pride Movement) said they expect thousands of people to join the caravan along its 10,000 km (about 6,000 miles) journey, which should end in New Delhi in late February.

On the way, the protestors, who are travelling by bus, plan to hold meetings with local officials and communities to encourage women to speak out about sexual violence.

"The objective is to turn shame to support," said Ashif Shaikh, convener of Rashtriya Garima Abhiyan.

In addition to raising awareness with their "dignity march", participants said they hope authorities will take steps to help sex crime survivors, including training police and doctors to be sensitive while recording cases and examining victims.

Access to support services like legal aid and healthcare is also poor, according to campaigners.

Mamta, a sex trafficking survivor who requested her last name be withheld, recounted a long wait for police to register her case, as well as intrusive medical tests and uncomfortable questions in court.

"Why is the burden of proof on me?" she asked, arguing that alleged perpetrators should instead be required to prove their innocence.

Mamta said she was raped by a family friend who then sold her for 200,000 rupees ($3,000) to a man who kept her as a slave in his house for nearly six months, until another resident of the village helped her escape.

When she returned, her husband rejected her.

"Instead of supporting me, my family abandoned me. Where will women like me go? I want to raise this issue at the rally," Mamta said.

Vikram Raghuvanshi, a father of another rape victim, said the rally would send a strong message to authorities and society in general.

"Until we don't speak about this crime openly, people will keep committing it," he told the Thomson Reuters Foundation.

"This has to stop."