The Hong Kong government ordered tests of all dairy products imported from the mainland.

Melamine was first found in baby formula produced by Hebei-based Sanlu Group, one of the three market leaders, but since last week it has been found in samples of baby milk from 21 other producers, including the other dairy giants, Mengniu and Yili. Adding melamine to milk makes its protein content appear higher.

Li Changjiang , head of the General Administration for Quality Supervision, Inspection and Quarantine (AQSIQ), said 5,000 inspectors in 1,400 teams had been sent to oversee all companies' processing of milk into baby formula.

The government would consider increasing imports of formula to meet shortages and helping manufacturers which meet safety standards to boost production.

Minister of Health Chen Zhu told a news conference 6,244 babies were now known to have fallen ill after being fed tainted formula, of which 158 were suffering from acute kidney failure.

A third death linked to tainted formula was reported in Zhejiang province , Mr Chen said, and more than 1,300 infants had received hospital treatment.

The minister said authorities had been aware of 'problems' in baby formula in mid-July but several investigations had failed to find the cause. He did not say which authorities he meant, nor explain why the public was not warned earlier even though the exact cause was not known. The central government says it only learned 10 days ago that tainted milk was causing kidney stones

AQSIQ said food producers would no longer be exempt from inspection under a scheme recognising high-quality products.

Under the scheme, companies whose products pass government inspection three times in a row are exempt from quality checks. Many of the tainted milk products were made by companies so exempted.

The State Council meeting chaired by Mr Wen admitted loopholes and dereliction of duty in the supervision of dairy product safety. The government would conduct tests of dairy products across the board and clean up the industry so that there was 'a fundamental change in [their] quality', Xinhua reported.

The government also promised to remove all substandard products from shop shelves and inspect each batch of dairy products before it leaves a production plant.

Yang Chongyong, vice-governor of Hebei, said the provincial government had inspected 372 milk collecting centres and found problems at 41.

Ji Chuntang , the deputy party secretary of Shijiazhuang , the Hebei capital where the Sanlu Group has its headquarters, was sacked yesterday and Sanlu chairwoman Tian Wenhua detained.

Mr Li said no melamine had been found in dairy products served to athletes taking part in the Beijing Olympics or the Paralympics, which ended yesterday.