New Zealand formally ratified the Trans-Pacific Partnership trade deal Thursday, becoming the second signatory country to do so after Japan, and just days ahead of Prime Minister Bill English's visit to Japan to promote trade and economic ties.

Trade Minister Todd McClay welcomed the Cabinet's decision to ratify the free-trade pact and said it showed leadership with Japan, which completed domestic ratification procedures last December, despite U.S. withdrawal from the deal.

Noting that the pact "remains valuable both economically and strategically," McClay said in a statement, "We are still actively exploring alternative options for TPP and expect other TPP partners to also ratify in the coming months."

New Zealand and Japan are among the 11 Pacific Rim countries that remain in talks over the future of the TPP after the United States pulled out of the pact shortly following President Donald Trump's inauguration in January.

Sources close to the negotiations have said some signatories including Japan and New Zealand are discussing the possibility of bringing it into force without Washington's participation.

McClay will accompany English on his three-day trip to Japan from Tuesday, during which the premier will meet his counterpart Shinzo Abe.

New Zealand is the depositary for the trade pact, which was signed in Auckland in February last year by 12 member nations.