Japanese firms that import dairy products from China have been ordered by the government to test them for melamine, a toxic chemical at the centre of a growing milk scandal.

Jiji Press said the order, which includes firms which use the products in processed food, came after melamine was found in four items made by one of Japan's leading food makers, which had earlier issued a recall as a precaution.

The Ministry of Health, Labor and Welfare order requires importers to test their goods at registered inspection institutions. Violators could face up to one year in prison or fines of up to one million yen (9,400 dollars), Jiji reported.

Japan's Marudai Food Co recalled more than 300,000 buns and other products last week fearing contamination by tainted Chinese milk.

A public health centre in Osaka Prefecture said four of Marudai's products were tainted by the chemical: Gratin Crepe Corn ready meals, Cream Panda and Matcha Azuki Milk Man sweet buns for consumers and Cream Panda buns for commercial use, Kyodo News reported.

Marudai said no consumers have complained of illness after eating its products, Kyodo reported.

The health ministry has also ordered the examination of drugs and cosmetics that contain Chinese-made milk, Jiji reported.

Japan's regional governors have asked Tokyo to suspend imports of all Chinese dairy products after tens of thousands of children fell sick in the country and four died after ingesting melamine, normally used to make plastics.