The woman arrested in Korea over the murder of two children found in suitcases in South Auckland had been holed up in a modern apartment complex owned by a metals company usually reserved for their workers.

The 42-year-old was arrested on September 15 after an early-morning stakeout by plainclothes police officers of a grouping of identical 15-storey buildings in the town of Onsan-eup within the South Korean port city of Ulsan, the Herald on Sunday can reveal.

New details of the circumstances around her arrest emerge as she awaits extradition back to New Zealand to face charges over the murders of two children, aged 7 and 10, in 2018.

New Zealand Police have confirmed they had made the extradition application and are working through the process with Crown Law.

The homicide investigation was launched after the remains of two primary school-aged children were discovered on August 11 in suitcases bought by the occupants of a property on Moncrieff Ave, Manurewa.

The suitcases were bought unwittingly as part of an online auction for the abandoned contents of a storage unit in the Safe Store facility in Papatoetoe, Auckland.

A grouping of identical 15-storey buildings in the town of Onsan-eup within the South Korean port city of Ulsan where the woman charged with murder over the death of two children was living.

Police launched a homicide investigation after human remains were found at a property in Clendon Park. Photo / Dean Purcell

Immigration records show the woman arrested over the murders arrived in Korea in July 2018.

Seoul's National Police Agency confirmed the woman arrested was accused of murdering her two children, but NZ Police have still not clarified this.

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The Herald on Sunday can reveal the apartment blocks from which she was arrested on September 15 shortly before 1am Korean time (4am NZ time) are owned by Korean metals and energy company Korea Zinc.

It's understood the woman lived in an apartment on the top floors of one of a grouping of five identical buildings. The company logo Korea Zinc can be seen printed on the side of one high-rise.

It is not clear if the 42-year-old was arrested directly at her apartment, or out the front of the buildings. But it's understood neighbours within the Korea Zinc apartment complex saw the woman being escorted by plainclothes policemen on September 15.

A woman, centre, was arrested in South Korea and now faces extradition to New Zealand.

Safestore facility in Papatoetoe where a Clendon Park family reportedly purchased the contents of a storage locker that contained human remains of kids. Photo / Jed Bradley

The Korea Zinc complex is reserved exclusively for employees of the company, but it's believed the 42-year-old did not work for them, and may not have been working at all in Korea since moving there in July 2018.

A source told the Herald this likely means the woman knew someone already living in the complex.

It can also be revealed the woman had relatives in Seoul who have been located.

As the 42-year-old was leaving Ulsan police station later on September 15 to be transported to Seoul, ushered by authorities, she was photographed with a hooded jacket pulled over her face.

The woman repeatedly said "I didn't do it", Korean media reported.

Ulsan is a port city on Korea's southeast coast with a population of 1.1 million.

"Police arrested the suspect at an apartment in Ulsan on Thursday following a stakeout with tips on her whereabouts and CCTV footage," Seoul's National Police Agency said in a statement.

Police at the Clendon Park property of Moncrieff Ave where the discovery was made by a resident. Photo / Jed Bradley

"The suspect is accused by the New Zealand Police of having murdered two of her children, aged 7 and 10 then, in around 2018 in the Auckland area," it said.

"She's been found to have arrived in South Korea after the crime and has been in hiding ever since."

Korean media have also reported the children were a boy and a girl.

Korean and New Zealand police in conjunction with Interpol managed to track the whereabouts of the woman in Ulsan via her medical records and phone number, many Korean media outlets have reported.

Detective inspector Tofilau Fa'amanuia Vaaelua said NZ Police applied to have her extradited to New Zealand to face murder charges and requested she remain in custody while awaiting completion of the extradition process.

"To have someone in custody overseas within such a short period of time has all been down to the assistance of the Korean authorities and the co-ordination by our NZ Police Interpol staff," Vaaelua said.

"In the meantime, there are a number of inquiries to be completed both in New Zealand and overseas."

Vaaelua said the investigation had received ongoing assistance from the South Korean Ministry of Justice, the South Korean Prosecution Service and the Korean National Police Agency.

Safestore facility aisle where a Clendon Park family reportedly purchased the contents of a storage locker that contained human remains. Photo / Jed Bradley

The woman remains in custody in South Korea and will undergo a review at the Seoul High Court over whether she should be extradited, Park Seung-hoon - an official at the National Police Agency - said following the arrest in September. Park said a date hadn't yet been set but the review must take place within two months from the arrest.

Korean police plan to hand over the woman to Seoul Central District Prosecutors' Office and an extradition review will be conducted at Seoul High Court.

At this High Court hearing, it will be decided if the woman will be extradited back to New Zealand.