Beijing  - China's agriculture ministry on Tuesday launched measures designed to rein in "out of control" milk purchasing depots, after at least 53,000 infants fell ill from drinking powdered milk tainted with the chemical melamine.

The ministry issued a notice requiring all milk dealers to register with the government and ordering regular inspections of milk to prevent any more tampering.

Agriculture Minister Sun Zhengcai was quoted on the ministry's website as saying that officials must respond to those who illegally adding melamine to milk "with the greatest determination and the toughest measures."

"Because milk stations only started operating in recent years, the country now has no specific method of supervising them, and no clear supervisory department," Sun said. "The purchasing process of raw milk is basically out of control."

The government on Monday said an investigation confirmed that the Sanlu company, the producer of much of the tainted milk powder, had covered up problems of melamine contamination for months.

It also sacked the top official for quality supervision and the mayor of Shijiazhuang, the capital of the northern province of Hebei, where Sanlu is based.

The company reported problems to the city government on August 2 but Shijiazhuang officials did not inform the provincial government until September 9, China Central Television said.

Sanlu had "covered up for months the contamination of its baby formula products", the official Xinhua news agency late Monday quoted an official investigation as saying.

The agency gave no details of the investigation, but earlier reports said Sanlu knew about the contamination of milk powder in March.

On Tuesday, Foreign Ministry spokeswoman Jiang Yu admitted that the central government was first informed about contaminated milk by the New Zealand government, apparently denying that her government had covered up the problem.

"On the morning of September 9, the New Zealand embassy informed China national quality inspection administration about the problem of Sanlu milk powder," Jiang told reporters.

"The national quality watchdog held an urgent meeting immediately and sent a special investigation team to Shijiazhuang," she said.

"That night the group sent back the initial results of their investigation, and carried on other relevant work," Jiang said.

The New Zealand dairy cooperative Fonterra owns 43 per cent of Sanlu.

Nearly 13,000 were hospitalized for problems linked to the consumption of tainted milk powder, state media said on Monday.

Four babies died and 104 were seriously ill with kidney problems, while 1,579 babies were discharged from hospital after treatment, the health ministry said.

Most of those under treatment had consumed baby milk powder made by Sanlu and 99.2 per cent of them were under three years old, it said.

Melamine is used as a binding agent and coating for particle, fibre and laminated board in furniture. It is also used to make fertilizer. (dpa)