BEIJING (NYTIMES) - The men and women wrestled Ms Wang Jianna to the ground. Holding down her legs and shoulders, they pried her six-month-old baby from her arms and took off running.

A surveillance camera captured it all. But there was little Ms Wang could do: The person leading the abduction on the street outside her mother's home was her partner, the baby's father.

The police in the northern Chinese city of Tianjin refused to get involved, according to Ms Wang, saying it was not possible for a parent to abduct his own child.

Then a court granted sole custody to Ms Wang's partner, citing a need to keep the baby in "familiar surroundings".

That afternoon in January 2017 was the last time Ms Wang saw her daughter in person.

"I feel deeply wronged," said Ms Wang, 36. "Although snatching is unreasonable and unjustified, the court still supported it."

Custody battles can be bitter affairs anywhere in the world. In China, where courts rarely grant joint physical custody, disputes over children are especially acrimonious.

Judges often keep children in their existing living environment, saying it is best for their well-being. But it creates a perverse incentive for parents going through a split to abduct and hide their children to win sole custody.

Nine months after Ms Wang's child was snatched, the police in Tianjin acknowledged in a final report that her partner, Mr Liu Zhongmin, had injured Ms Wang and her mother during a "physical dispute over a child", according to a copy of the report viewed by The New York Times.

The police ordered Mr Liu to serve a 10-day administrative detention and pay a fine of about US$75 (S$102) for causing physical harm. But the officers did not blame him for taking the child.

Mr Liu could not be reached for comment. His lawyer and one of the people alleged to have been involved in snatching the child hung up the phone when asked for comment.

For decades, Chinese law did not make it a crime for parents to kidnap and conceal their own children.

The problem has become more widespread as the country's divorce rate has steadily risen.

Most divorces in China are settled privately, which can result in custody-sharing agreements. But for couples who go to court, it is often all or nothing.

In June, the government sought to address the problem by outlawing abductions for custody purposes. Activists welcomed the law but said it was too early to tell whether it would make a difference.

An estimated 80,000 children were abducted and hidden for custody purposes in 2019, according to a recent report by prominent family lawyer Zhang Jing, citing figures released by China's highest court.

Many say the figures are most likely higher. A long-time judge in the southern Chinese city of Guangzhou told state news media in 2019 that more than half the contested divorce cases she saw involved the abduction of a child for custody purposes.

More often than not, fathers are behind the kidnappings. Men were responsible in more than 60 per cent of such cases, the lawyer in Beijing found. The abductions involved mostly sons under age six, reflecting the traditional emphasis in China on boys as carriers of the family name.

"It's become almost a game - whoever has physical custody has legal custody," said Ms Dai Xiaolei, who founded Purple Ribbon Mother's Love, a grassroots advocacy group, after losing a custody battle with her former husband. "It's a free-for-all."

In some cases, abducting children in a bid for custody is part of a broader pattern of domestic violence. Official statistics show that about one in three families is afflicted by domestic violence.

Disputes over custody have only recently become a major issue in China. Traditionally, a woman seeking a divorce was expected to forgo custody of her children. But that has changed over the years as women in China have gained more financial stability and independence.

On paper, Chinese law is tilted slightly in favour of women. In cases in which the child is two years or younger, mothers are typically awarded sole custody.

But in practice, judges can be swayed by institutional and informal considerations that experts say often give men an advantage. For example, men have access to more financial resources and property, allowing them to make a stronger claim for custody.

"The law itself looks very neutral, but many things behind it are not equal," said University of Hong Kong law professor He Xin. "Women often lose out."

Not long after Ms Wang's former partner took their daughter, he cut off all contact.

Last year, Ms Wang persuaded a court to force him to hand over photos of their daughter. They show a toddler with pigtails and piles of colourful toys. But the child's face is obscured - a strategy, Ms Wang believes, that was devised by her former partner to prevent her from one day recognising their daughter and snatching her back.

Four years later, she still dreams of reuniting with the baby she once rocked to sleep every night.

"If I'm not saving her in my dreams, then I'm chasing after her," Ms Wang said. "But her face appears as a blank - I have no idea what she looks like."