China is pressuring New Zealand to do more to help apprehend officials it claims are corrupt and who have moved to this country with their money, Prime Minister John Key says.

Photo: RNZ / Diego Opatowski / Pool

New Zealand has no extradition treaty with China, mainly because it has the death penalty.

Mr Key said President Xi Jinping told him during his recent visit to New Zealand there were a number of people China wanted returned to face justice, whom it suspected of fleeing the country with money earned from corrupt activities.

"They're certainly keen to get a few people back from New Zealand, but at this point I'm not aware of formal cases with the exception of one, and the one formal case that I'm aware of is not related to inappropriate gain of funds, it's a completely different issue," he said.

That person was suspected of inappropriate sexual behaviour and would probably be returned to China - as long as New Zealand could be confident they would not be tortured or put to death.

That would apply to anyone returned to China, Mr Key said.

When pressed about the number of people China wanted returned for corruption, Mr Key would only say it was a "reasonable" number.

Mr Key said it was an issue which was raised by the Chinese, and the New Zealand response was very much in the preliminary stages.

It could be difficult to ascertain whether people were entering New Zealand with ill-gotten gains, and immigration officials did their best at the border to make sure any funds were legitimate, he said.