Prime Minister John Key has admitted he misled reporters over Cabinet Office advice about a controversial visit by Justice Minister Judith Collins to a Chinese company associated with her husband while on an official trip to China.

On Monday Key told media the Cabinet Office had cleared Collins of a conflict of interest after translating comments on Oravida's website which stated that she had praised its products.

But today Key's office confirmed that the Cabinet office had only read the English language version on the website, which did not contain those references.

A spokesperson for Key said the Cabinet Office had been asked for guidance on the issue and its advice was clear that there was no conflict of interest and no endorsement.

"As the advice referred to the material on the company's website, the prime minister took that advice to apply to both the English and the Chinese translation."

He had become aware last night, however, that was not the case.

"The Cabinet Office later became aware the Chinese translation differed from the English version, but by then Minister Collins had already asked the company to remove the Chinese version and Cabinet Office considered the appropriate remedy."

However, the Cabinet Office stood by its advice that there was no conflict of interest and Collins had not breached the cabinet manual, which states that ministers must not endorse products in any media.

Collins' husband, David Wang Tung, is a director of the company, which exports milk products to China and has previously donated to the National Party.

Key repeatedly defended Collins last week, refuting claims that she had endorsed Oravida.

When quizzed on Monday about whether he was sure the Cabinet Office had looked at a translation of the Chinese statement which contained the endorsement claims, Key said he was.

"Yes, they looked at the translation."

Labour MP Grant Robertson accused Key of misleading the public.

"John Key has been covering up for Judith Collins for the past week.

He told New Zealanders the Cabinet Office had looked at a translation of the Chinese company's webpage detailing her visit," he said.

"That is simply not true. John Key has been caught out."

Robertson said the Cabinet Office had not looked at "the most important piece of evidence to ascertain whether Judith Collins had a conflict of interest - the Chinese translation which says Judith Collins was 'full of praise' for Oravida's products".

"It is clear to most New Zealanders that Judith Collins endorsed her husband's company while on a taxpayer-funded trip. This is a conflict of interest."