India has long outlawed child marriage but hasn't been able to enforce the law. (Representational)

Home to a third of the world's child brides, India is set to change the law that is seen to legitimize child marriage and treat every marriage in the future involving minors to be invalid.

The proposal is expected to come up for approval of the union cabinet headed by Prime Minister Narendra Modi shortly. It would go a long way to promote the well-being of the girl child, a government source told NDTV.

According to the proposal likely to be sent to parliament soon, the government intends to treat every child marriage "null and void".

India has long outlawed child marriage but hasn't been able to enforce the law, first enacted in 1929. The Child Marriage Restraint Act fixed the age of marriage for girls at 14, and boys at 18 years. It was last raised to 18 years for girls in 2006.

It has been crime to marry off minors but the law gave the young couple the right to decide if they wanted to stay married. If they didn't, the minor could get it voided. Else, it was as good as any.

But in a country where child marriages have social acceptance - BJP's Madhya Pradesh legislator Gopal Parmar even prescribed early marriage to prevent girls from eloping - the enforcement of the law has, at best, been patchy.

In 2014, there were all of 280 complaints of child marriages. In 2016, there were a little over 320 cases.

Advocacy group ActionAid estimates India contributes 33 per cent of the total number of child brides in the world with nearly 103 million Indians married before they were 18. The UN population fund has

The world child body UNICEF, which calls child marriages a death sentence for the girls, estimates that 27 per cent of girls, or nearly 1.5 million girls, get married before they turn 18 in India.

It is still better than the 47 percent a decade ago though.

Officials say there were very few girls or women who actually used the law to get their child marriage annulled. It is unusual to find people such as 18-year-old Pintudevi from Rajasthan, who recently got her marriage dissolved despite threats from her in-laws.

The Supreme Court had taken a huge step last year when two judges, dismayed by estimates that there were 23 million child brides in the country, criminalised sex with a minor wife.

"A perusal of the various reports and data placed before us clearly shows that marriage of the child not only violates the human rights of a child but also affects the health of the child," the bench said.

These women are also more likely to be victims of domestic violence, sexual abuse and social isolation.