New Zealand is working on a "Plan B" to the 12-nation Trans-Pacific Partnership (TPP) trade deal and China's involvement is possible, Prime Minister Bill English said Monday.

United StatesPresident Donald Trump's decision to withdraw from the still-unratified TPP would not necessarily stop the other 11 nations working on a modified version of the deal, English told Radio New Zealand.

New Zealand passed legislation late last year allowing the government to ratify the agreement, which was signed in Auckland in February last year.

English said the Trump administration's "America first" trade policy was "not in our interests and we would argue it's not in America's interests in the long run either, but they've made a pretty clear policy decision."

"So we're working on Plan B. It was promising that last week the Prime Minister of Japan, when he was in Australia, made quite a positive statement about trying to proceed with a version of the TPP without the U.S. in it, if it comes to that," said English.

"We don't believe it's dead, but Plan B could be a bit tricky."

Asked if it was possible the TPP could be scrapped and replaced with something else, possibly involving China, English said, "That's possible."

"There are other vehicles for China if they've got an interest in free trade in the Asia-Pacific, but the TPP's a fairly original, a fairly unique kind of trade agreement and there are real benefits in it for New Zealand if we can just get everybody organized," said English.

New Zealand Trade Minister Todd McClay would probably visit Washington "before too long" and begin talks with his counterparts in other TPP countries over the next couple of months about an alternative to the current agreement.