The Supreme Court has ruled a New Zealand resident accused of murder in China can be extradited there without any real risk of torture or unfair trial.

Kyung Yup Kim, 46, is accused of murdering 20-year-old woman Pei Yun Chen while visiting Shanghai in 2009.

On Wednesday, by a majority of three to two, the Supreme Court set aside a Court of Appeal ruling quashing the extradition and reinstated the former justice minister Amy Adam’s earlier decision to surrender.

Kim’s lawyer Tony Ellis said Wednesday’s decision was disappointing and a “step back” 10 or 20 years. He argues Kim faces the risk of torture and unfair trial in China but the Supreme Court said sufficient diplomatic assurances have been provided by China that this won’t happen.

“It’s a very bad decision in the context of international human rights law. Nobody except New Zealand will have extradited anybody from a western country in the last 10 years or so because of the state of affairs in China. So it’s quite alarming really,” Ellis said.

Otago University law professor Andrew Geddis said the decision seems “remarkably trusting” of the word of China, a country he points out is denying genocide in Xinjiang Province.

The justice minister Kris Faafoi is now considering the judgement.

“It opens the way for China to request the extradition of others claimed to have offended in China, including those accused of "corruption" and other more political crimes,” Geddis said.

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Justice Minister Kris Faafoi can choose whether he stands by the previous National minister Amy Adam’s decision to extradite.

Geddis said the decision is likely to be a relief for the Government.

“The Supreme Court has (in effect) said that China's Government can be trusted to stick to its promises to treat Mr Kim in accordance with international human rights standards and proper procedures of justice. It would have been harder for it had the Supreme Court said otherwise - that China (in effect) is not to be trusted."

Ellis has asked the minister not to extradite his client on the grounds of deteriorating health. Kim has a brain tumour as well as kidney and liver disease, and Ellis has said he won’t get adequate medical treatment in Chinese jails.

Ellis is also lodging a complaint before the UN Human Rights Council, accusing New Zealand of breaching international law.

“Whether the Government holds off actual deportation until those institutions make their views known will be the next big question,” Geddis said.

It's the first time China has asked New Zealand to extradite one of its citizens or residents. New Zealand, like many Western countries, does not have an extradition treaty with China.

The case has been in and out of the courts since China first made the extradition order in 2011. Kim spent five years in prison on remand, but is now on bail to his home in Auckland.

Chinese police say they have forensic evidence, but Kim denies the accusation and claims to have a defence.