A tearful reunion between a mother and her dead daughter via advanced virtual reality for a South Korean television has become an online hit, triggering a fierce debate about voyeurism and exploitation.

The footage began with the girl - who died of leukaemia in 2016 - emerging from behind a pile of wood in a park, as if playing hide-and-seek.

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"Mum, where have you been?" she asks. "I've missed you a lot. Have you missed me?"

Tears streaming down her face, Jang Ji-sung reached out towards her, racked with emotion.

"I have missed you Na-yeon," she told the computer-generated six-year-old, her hands moving to stroke her hair.

But in the real world, Jang was standing in front of a studio green screen, wearing a virtual reality headset and touch-sensitive gloves, her daughter's ashes in a locket around her neck.

At times the camera cut to Jang's watching husband and their three surviving children, wiping away tears of their own.

A nine-minute clip of the Munhwa Broadcasting Corporation (MBC) documentary, I Met You, has been watched more than 13 million times in a week on YouTube.

Many viewers offered Jang their sympathy and support for the concept.

"My mother unexpectedly passed away two years ago and I wish I could meet her through virtual reality," said one.

But media columnist Park Sang-hyun said the documentary amounted to exploitation of personal pain.

"It's understandable a grief-stricken mother would wish to meet her late daughter. I would do the same," he told the AFP news agency.

"The problem lies in that the broadcaster has taken advantage of a vulnerable mother who lost a child for sake of the viewer ratings."

"If the mother had been counselled before the filming," he added, "I wonder what kind of a psychiatrist would approve this."

It took eight months of filming and programming to create the virtual Na-yeon, but the makers of the documentary insisted the broadcast was intended to "console the family" rather than promote virtual reality in ultra-wired South Korea.

The technology presented a "new way to keep loved ones in memory", one of the producers told reporters.

Jang herself - who has her daughter's name and date of birth tattooed on her arm in memory - hoped the programme could "console" others who had lost loved ones.

"Even though it was a very brief ... I was really happy in the moment," she wrote on her blog - which she has since turned private.

During the broadcast the two sat at a table to celebrate Na-yeon's missing birthdays, singing "happy birthday" together.

Before blowing out the candles, Na-yeon made a birthday wish: "I want my mother to stop crying."