BEIJING (AFP) — China insisted on Wednesday that it was being open about the impact of milk tainted with the toxic chemical melamine, but declined to make public the latest data on how many children had fallen ill.

As the World Health Organisation issued a statement stressing the need to share health information in a timely manner, Chinese officials said they were not yet ready to reveal any updated figures.

"I have not been authorised today to make announcements about the number of sick children," health ministry spokesman Deng Haihua told a briefing on the government's latest efforts to contain the scandal.

Data that have not been updated since September 22 show melamine-tainted milk has killed four children in China and sickened 53,000, triggering an alert that has seen many countries and suppliers around the world curb or restrict Chinese dairy imports.

These figures have now been overtaken by new national data, health ministry officials admitted this week -- while insisting they were not ready to share them with the public.

Deng defended the ministry's approach, arguing it had been forthcoming so far.

"Since the Sanlu baby formula case emerged, the health ministry has on four occasions announced the number of children affected by the problem milk," he said, referring to Sanlu Group, the company at the centre of the scandal.

He said the new figure would be made public "at an appropriate time."

In its statement, the WHO noted that on public health issues, "the prompt sharing of information is important."

"China continues to handle the care of these infants and the safety of the food supply in an appropriate and diligent fashion. We would expect that in due course, Chinese officials will release the relevant figures into the public record," it said.

Hans Troedsson, the WHO's representative in China who frequently meets with local authorities, said the health ministry had not yet passed on new numbers -- but that the UN body had not asked for them either.

"I don't know the reason why they don't want to do it. I don't see why they couldn't share it," he told AFP.

"But to be honest, I don't know the reason why they don't share it, because it hasn't been discussed with them."

"We will of course ask for the number and also if they don't want to go public with it, we will also ask them why, but we will of course respect that if they have a good justification," he added.

He said authorities might have good reasons to keep figures to themselves if, for instance, they are not yet verified.

Separately, China announced limits for how much melamine its dairy products can contain, setting the maximum at one milligram per kilogram of baby formula and 2.5 milligrams per kilogram for other dairy products.

"Melamine is not a food raw material, and it's also not a food additive," said Wang Xuening, deputy director general of the health ministry's health supervision bureau.

"We prohibit people adding it to food items. Cases where melamine has been added to food will be investigated according to law," he told a briefing in Beijing.

Melamine is an industrial chemical used for producing plastic, but when added to milk, it makes it look richer in protein than it really is.

Officials at the briefing did not say directly how the new legally allowed amount of melamine may come to be in the dairy products.

But Chen Junshi, a senior researcher at the National Institute for Nutrition and Food Safety, pointed out that the chemical was often used in packaging used for food products.

China's product quality watchdog Wednesday published the findings of a new check of milk powder products, saying it had found no traces of melamine, the China News Service reported.

A total of 219 batches of baby formula were inspected along with 97 batches of other types of milk powder, according to the General Administration of Quality Supervision, Inspection and Quarantine.

The fallout of the milk scandal has continued to spread, with Brazil on Tuesday becoming the most recent country to react, banning imports from China of food products containing lactose or milk.

And officials in the Philippines on Wednesday said a third Chinese-made milk product sold there had tested positive for melamine, and ordered it off store shelves.