Beijing is taking appropriate action to deal with the melamine contamination of its milk supplies, the World Health Organisation's representative in China told just-food today (22 September).

Dr Hans Troedsson's comments came just hours before China's chief quality supervisor, Li Changjiang, stepped down over the growing safety scare, according to a report in the official Xinhua state media.

Four babies have died and nearly 13,000 remain in hospital after drinking milk powder containing the industrial chemical melamine.

Dr Troedsson called the crisis a "serious food safety issue" but said the government "has taken appropriate action both by informing the public and widening the investigation".

Beijing is providing the WHO with daily updates on its investigation into the issue, which Dr Troedsson said has been "very well co-ordinated".

He admitted, however, that it is still unclear whether officials could have acted earlier.

"The central government told me they were informed in early September. What is still under investigation is what the local authorities knew before this."

Fonterra, a minority owner of Sanlu, the dairy that first revealed the problem, said that it became aware of the contamination in early August. Local media reports say that Sanlu began its own tests in July.

China needs to strengthen surveillance of the industry "at the local level", said Dr Troedsson. "There's a need for some improvement and the Chinese government has recognised this."