Chinese food safety personnel check on the fresh milk at a collection station. ((Color China/Associated Press))

Chinese officials have detected unacceptable levels of melamine in 31 more batches of milk powder, according to a government website on Wednesday, and advised the public to stop consuming certain products.

The contaminated milk widens the tainted milk scandal to 15 more Chinese dairy companies accused of violating the legal limit of 2.5 parts per million of melamine.

The new batches being tested were mostly milk powder products for adults. A previous round of tests found melamine in 69 infant milk powder batches.

"Based on the levels detected, the public is advised to stop consuming the products concerned," a spokesman with China's Centre for Food Safety said in a press release.

"We are closely monitoring the situation and will continue to collect other dairy products and products with dairy ingredients for testing," said the release.

The tests found that products involved in the Cadbury Asia Pacific recall were safe.

Previous test results sparked product recalls in China and a host of other countries that received Chinese food exports.

Melamine is used to make plastics and fertilizers. It is high in nitrogen and when added to food products can mask low nutrient levels in standard tests.

Some experts have said some of the contamination could come from the environment during food processing, but others speculate Chinese producers may have added melamine to watered-down milk.

Consuming it can cause kidney stones and kidney failure. Infants are particularly vulnerable.  

Melamine contamination in infant formula, fresh milk and other milk products in China and has been blamed for the deaths of four children, and caused kidney ailments among 54,000 others. More than 13,000 children have been hospitalized.

So far 27 people have been arrested in connection to the contamination.

At least 100 batches of milk powder have been found to contain melamine, according to Chinese food safety website.

A round of testing announced on Sept. 16 found melamine in 69 milk powder batches and 24 batches of liquid milk produced by three of the country's best-known dairy firms.

Prior to Sept. 14, 265 batches of milk powder produced by 154 of China's 290 milk powder producers had been tested.

Nine of the batches most recently found to contain melamine were produced by Sanlu Group, a key player in the scandal and in which New Zealand dairy co-operative Fonterra holds a 43 per cent stake.

No date for the testing was given.

Cookies, cheese cake contaminated

Also on Wednesday, Hong Kong's food safety agency said melamine was found in Lotte Cream Cheese Cake, a Japanese brand made in China.

Hong Kong and Macau authorities have also detected excessive melamine in Lotte's popular Koala's March chocolate and strawberry cream cookies.

The levels of melamine discovered in batches tested so far have varied widely, from as much as 6,196 milligrams per kilogram to as little 1.3 mg/kg.

Chinese health officials have said it is safe to consume less than 0.63 mg/kg of body weight per day.

For children under the age of 36 months the level is 0.32 mg/kg of body weight per day.

An example from the food safety centre indicated that based on recent samples of cookies that had a detected level of 43 ppm of melamine, a child weighing 10 kg would have to eat about 0.07 kg, or about 1.5 packs of the cookies each day to reach an unacceptable level.

An adult with average body weight of 60 kg, would need to consume about 0.9 kg, or 17 packs of the cookies a day.

"We have informed the trade of the test results and asked them to stop selling the products with unsatisfactory results," said the release. "We have also sent warning letters to the importers and retailers concerned, and the importers would recall the affected products."

With files from the Associated Press