Prime Minister John Key met his Japanese counterpart for half an hour last night in talks which focussed on Japan signing up to the Trans Pacific Partnership trade negotiations.

In April, Prime Minister Yoshihiko Noda formally declared Japan's interest in joining the TPP talks in November.

But he faces growing campaigns from supporters and opponents of Japan's proposed TPP participation.

New Zealand - a member of the TPP - wants a high quality and comprehensive free trade arrangement, including agricultural products, which in Japan are charged prohibitive duties.

The Government has been concerned the United States might concede ground to get the Japanese on board.

Mr Noda told Mr Key that Japan would join "under the right conditions".

Mr Key declined to reveal those conditions.

Trade analysts say New Zealand would make large gains if Japan and South Korea are in the TPP.