Fitch Ratings assigned bonds a "AAA" rating with a stable outlook to Westpac New Zealand's 750 million euros in series 2025-1 fixed-rate mortgage-covered bonds, the credit ratings agency said Thursday.

The rating on the mortgage-covered bonds is based on Westpac New Zealand's long-term issuer default rating of "A+," the uplifts above the issuer default rating granted to the program, and the overcollateralization protection provided through the program's asset percentage, the agency said.

The stable outlook reflects a three-notch buffer against an issuer default rating downgrade.

The bonds will be issued through Westpac Securities NZ's London branch and have a 12-month extendable maturity.

Westpac's Australia and New Zealand shares were each down 1% in recent Thursday trade.