Two New Zealand government ministers on Wednesday insisted they were working to overturn bans by Russia, Belarus and Kazakhstan on New Zealand dairy products, as criticism of the government's handling of the Fonterra botulism crisis continued.

Trade Minister Tim Groser and Primary Industries Minister Nathan Guy said officials were working closely with Russian authorities to provide the reassurance they needed over New Zealand dairy products.

"Russia has formally notified New Zealand of a temporary restriction of dairy imports from 61 of the 83 dairy plants approved for export to Russia," Groser said in a statement.

"Overnight, New Zealand officials in Moscow have confirmed that the restriction is now also being applied by Kazakhstan and Belarus. As the three countries are in a Customs Union, this is not unexpected."

Guy said no potentially contaminated product had been exported to Russia, Kazakhstan or Belarus.

"However Russia has taken a precautionary approach, and we are now working to reassure the appropriate agencies of all the steps being taken," Guy said in the statement.

The main opposition Labor Party's trade spokesperson, Clayton Cosgrove, said New Zealand officials had failed to answer questions last week from the Russian Federal Service for Consumer Rights Protection.

"Officials were too slow to reassure the Russians that there were no issues with Fonterra products. Russia now requires a new inspection of almost all New Zealand dairy products. This will not happen until next year at the earliest," Cosgrove said in a statement.

Fonterra, the world's biggest dairy company, and the Ministry for Primary Industries announced early this month that 38 tons of whey protein concentrate had been contaminated in May last year with a bacterium that can cause botulism.

A series of inquiries by the government and the company have been launched to examine the causes and handling of the contamination and the ensuing consumer and trade crises.

New Zealand dairy exports to Russia last year were valued at about 106 million NZ dollars ($84.57 million) and those to Kazakhstan at 310,608 NZ dollars, but virtually no New Zealand dairy products were exported to Belarus.