Wellington  - The New Zealand dairy co-operative that owned a large stake in the Chinese company responsible for selling contaminated milk that killed six babies and made nearly 300,000 more ill refused all comment Friday on death sentences handed down to two people involved in the scandal.

A spokesman for the Fonterra co-op, which is the world's biggest single exporter of dairy products, said only, "We are still studying the verdict and are therefore not in a position to comment on any details."

A man who ran a workshop that was China's largest source of melamine, the toxic substance illegally put into baby milk powder to boost its protein content, and another who produced and sold toxic food were sentenced to death by a Chinese court on Thursday.

Tian Wenhua, 66, who was chairwoman of the Sanlu company, which was 43 per cent owned by Fonterra, was sentenced to life in prison.

Questioned on the rulings by reporters, New Zealand Prime Minister John Key said, "The New Zealand government does not condone the death sentence but we respect their right to take a very serious attitude to what was extremely serious offending."

The opposition Green Party foreign affairs spokesman Keith Locke called on the government and Fonterra to speak out strongly against the death sentences.

"They show the harshness of the regime towards anyone who embarrasses it, whether they are real criminals, whistleblowers or dissenters," he said.

"Many Chinese knew the milk was being contaminated but said nothing for fear of repercussions from those in authority.

"Fonterra could not get any action from local officials when it first discovered the contamination. There was only movement, some time later, when the matter became public."

Locke said New Zealand companies operating in China had a vested interest in promoting more democracy because the lack of transparency of the Chinese system created many problems for their operations there. (dpa)