Feb 3 (Reuters) - Shares in New Zealand's Fisher & Paykel Healthcare FPH.NZ were set for their worst session in 21 months on Monday as the medical equipment maker warned of higher costs arising from the U.S. imposing tariffs on imports from Mexico.

The stock dropped as much as 8.5% by 2216 GMT and was set for its biggest single-day fall since May 2023. It was the top loser on the S&P/NZX 50 index .NZ50, which was down 1.8%.

U.S. President Donald Trump on Saturday imposed 25% tariffs on Mexican and most Canadian imports and 10% on goods from China, starting on Tuesday.

Fisher & Paykel Healthcare, which manufactures about 45% of its volume in Mexico, received 43% of its revenue in the first half of fiscal 2025 from the U.S. Moreover, about 60% of its sales to the U.S. are supplied from its Mexican facilities.

As a result of the new tariffs, the company's costs would likely increase from fiscal 2026 onwards, it said. The tariffs may have added two to three years to its goal of achieving a gross margin of 65%.

"The company takes a long-term view and will be working with global suppliers and U.S. customers to provide solutions to best mitigate the impact of the tariffs on all parties," CEO Lewis Gradon said.

The Auckland-based firm's stock is down 10% so far this year, including the day's moves.

(Reporting by Aaditya Govind Rao in Bengaluru; Editing by Lisa Shumaker)

((Aaditya.GovindRao@thomsonreuters.com;))