Prime Minister John Key believes the Labour has a lot more than $15,000 in donations from wealthy Chinese political donor Donghua Liu.

He also acknowledged he had known for some weeks that Labour leader David has written a letter supporting Mr Liu's application for residency.

The release of the letter yesterday in the face of denials from Mr Cunliffe that he wrote any such letter has thrown his leadership into crisis.

It followed revelations earlier this week that Mr Liu donated $15,000 to Labour in 2007.


It did not show up in the donations register although that may have been lawful at the time.

A new poll will fuel Labour's crisis, with the poll today recording a 6 point plunge by Labour to 23 per cent. National is on 56 per cent.

Speaking from the East Lawn at the United Nations this morning, Mr Key said he had heard rumours that Mr Liu had given more that $15,000.

"I've heard the rumours and we'll see what actually comes out but I'd be very, very amazed if the amount is $15,000," he told New Zealand reporters.

"That's for the Labour Party to make clear to the New Zealand public."

Mr Key said he believed that people made mistakes in political life "but the realty is that there has never been the proposition he has been prepared to accept."

Mr Cunliffe had been asked the question about Donghua Liu on numerous occasions, not just once.

"It is very incumbent on you once the question has been asked once to go away and turn over every piece of paper and make sure the answer is right and if it not right, to correct and you've seen me on a number of occasions have to go and correct it."


Read the David Cunliffe's letter to Immigration about Donghua Liu here