About 7,200 dairy cows will depart New Zealand for China next week in what is believed to be New Zealand's largest-ever shipment of live cattle, Radio New Zealand reported Wednesday.

The cattle will depart the South Island port of Timaru on a three-week journey that has stirred a debate over ethics of exporting live animals.

South Island Dairy Farmers managing director Paul Brown told Radio New Zealand that the protocols in place to ensure the animals' safety had been developed by animal welfare experts.

New Zealand exported about 20,000 live cattle each year on modern ships equipped with ventilation and watering systems, and the animals are watched continually by veterinarians, Brown said.

However, the opposition Green Party said exporting thousands of live animals was cruel and needed to be more tightly controlled.

Green Party MP Julie Anne Genter said New Zealand could sell stock to other countries by exporting genetic material.

Mechanical or customs problems could keep animals stuck on ships in terrible conditions, she said in a statement Wednesday.

"Last year 22,000 Australian sheep were stuck on a ship in the Persian Gulf for a fortnight after the cargo was rejected by Bahrain," Genter said.

"In the current review of the Animal Welfare Act, the government has proposed the long overdue development of enforceable standards for live animal exports. We support this proposal, but they need to also include a focus on reducing these cruel live exports."