Beijing - Chinese authorities found an industrial chemical contaminating 12 per cent of dairy samples in a series of tests it is undergoing after tainted milk products started sickening babies, a news report said Wednesday.

The latest tests showed 31 of 265 batches of dairy products tested contained melamine, the official Xinhua news agency reported.

President Hu Jintao vowed the government would provide better oversight of the dairy industry on a visit to two dairy firms in east-central China.

"Food safety is directly linked to the well-being of the broad masses and the competence of a company," Hu said in Anhui province, according to state media reports. He added that the country needed to learn from the scandal of melamine-contaminated dairy products.

Melamine - which is used to produce fertilizers, pesticides and plastics - was first discovered in baby formula last month when infants began coming down with kidney problems. Four have died and 53,000 have been made ill. About 10,000 remain in hospital.

The chemical is added to low-quality or watered-down milk to boost its protein content and fetch a higher price.

Agriculture Minister Sun Zhengcai promised that the government would establish uniform supervision of all milk-procurement stations in the country.

"We will examine each and every milk procurement station and stamp out the practice of adding melamine to fresh milk," he said.

Chinese authorities began testing baby formula and then expanded their testing for melamine to fresh milk, yogurt and other dairy products.

Nearly a million tests have been conducted, and more than 8,200 tons of milk products removed from circulation. Two dozen milk firms have been affected.