China has banned all imports of milk powder from New Zealand after its main dairy exporter, Fonterra, found a bacterial strain in some of its products that can cause botulism.
China relies on New Zealand for almost all its imports of milk powder.
Imports are highly prized in China after a tainted milk formula scandal in 2008 killed six babies and made some 300,000 infants ill.
New Zealand's trade minister described Beijing's decision as "appropriate".
Fonterra's announcement that it had found the contamination led to a global recall of up to 1,000 tonnes of dairy products across seven countries, including China.
The potentially tainted products included infant milk formula, sports drinks, protein drinks and other beverages.
Botulism is one of the most dangerous forms of food poisoning, often leading to paralysis.
The bacteria was found in three batches of Fonterra's whey protein used in infants' Nutricia Karicare follow-on formula, Fonterra said.
Nearly 80% of dairy products imported by China come from New Zealand, according to state media.
Any prolonged ban of imports could well lead to a dairy shortage in China, the BBC's Martin Patience reports from Beijing.
New Zealand Trade Minister Tim Groser said China's action was "entirely appropriate".
He said: "It's better to do blanket protection for your people then wind it back when we, our authorities, are in a position to give them the confidence and advice that they need."
The Chinese authorities named four domestic companies that have imported potentially contaminated products from New Zealand. According to state media, these companies have begun a recall.
The whey product was produced in May last year, with a dirty pipe at one of Fonterra's processing plants in Waikato responsible for the contamination, the company said.
Fonterra, the fourth largest dairy company in the world, said it had urged its customers to urgently check their supply chains.
The countries affected besides New Zealand and China include Australia, Thailand, Malaysia, Vietnam and Saudi Arabia.
Russia is also reported to have begun a recall of Fonterra products.
Fonterra said there had been no reports of any illness linked to the affected whey product.
The dairy industry powers New Zealand's economy, with the country exporting up to 95% of its milk.