A 42-year-old woman has been extradited from South Korea to New Zealand, where she is to appear in court charged with murdering two children whose remains were found in suitcases sold at auction.

New Zealand police said that "three police officers travelled to South Korea to transport the woman", who arrived at Auckland Airport in the afternoon and was taken to Manukau Police Station.

Seoul's justice ministry said that key evidence in the case had also been handed to New Zealand officials.

"We hope that the truth of this case, which has received worldwide attention, will be revealed through a fair and strict judicial process in New Zealand," said an official in Seoul.

The suspect is due to appear in court on Wednesday, a police spokesperson said.

"She will be held in custody overnight when she will then be expected to appear in the Manukau District Court on two charges of murder," police added.

South Korean police arrested the suspect in the port city of Ulsan in September, weeks after New Zealand police discovered the remains of two school-aged children in Auckland.

Counties Manukau Police Station, where the woman has been taken

Images in Korean media at the time of her arrest showed the woman, who South Korean police have identified only by her surname Lee, being led out of an Ulsan police station by plainclothes investigators, covering her head with a large brown coat.

When asked by reporters whether she would confess to the killings, the woman repeatedly said "I didn't do it" as she was led into a police vehicle.

The bodies were discovered in south Auckland after an unsuspecting family bought a trailer-load of items - including the suitcases - at an auction for abandoned goods.

New Zealand police have said the bodies were likely in storage for several years, which has complicated the investigation.

Authorities have repeatedly stressed that the family who found the bodies were not connected to the homicides and were being given support to help deal with the trauma.

The office of New Zealand's Prime Minister declined to comment, but earlier this month, Jacinda Ardern said an extradition agreement between the countries ensured "our justice system can operate" in what she described as "a tragic set of circumstances".