• Three babies dead and more than 6,000 taken ill • 18 suspects arrested over scare and 87 questioned

This article is more than 12 years old

This article is more than 12 years old

Police in China arrested 12 more people today as investigations continue into a milk powder scandal that has killed three babies.

More than 6,000 infants in the country have been taken ill since being fed batches of contaminated milk formula last week. Local officials knew about the problem for more than a month before they alerted central authorities, it emerged yesterday.

So far, 18 suspects have been arrested in connection with the health scare, while a further 87 people have been summoned for questioning.

News of the contamination first began with reports that dozens of babies in Gansu province had developed kidney stones after drinking a milk formula that contained melamine, a chemical normally used in plastics.

Officials said that subsequent tests found affected batches at 22 of China's 109 milk powder manufacturers, including its two biggest dairies, Mengniu and Yili Industrial Group.

The number of affected infants has soared. The health minister, Chen Zhu, said that 6,244 babies had fallen ill, 1,327 were in hospital and 158 were suffering from acute kidney failure. He expected the number of cases to rise.

Chen said that so far all the sick infants had consumed milk powder made by the Sanlu group, the country's biggest formula producer. Li Changjiang, the head of China's quality control agency, said that 5,000 inspectors would monitor companies and all dairy products would be tested for melamine.

The chemical is banned from use in food, but adding it to watered-down milk makes the liquid appear higher in protein when tested.

China has sought to tighten its safety regime after a number of product scares. In 2004, more than 200 infants suffered malnutrition and at least 12 died after being fed formula containing no nutrients, and an estimated 1,500 dogs and cats died in the US last year after they consumed a melamine-tainted pet food ingredient manufactured in China.

The Sanlu case is particularly alarming because the recall took so long, and apparently required the intervention of the New Zealand government, which was alerted by Sanlu's New Zealand-based partner Fonterra. New Zealand's prime minister, Helen Clark, said on Monday that she ordered her officials to leapfrog regional authorities and inform Beijing directly.

Today, Shi Guizhong, a spokesman for the Hebei provincial police, said government officials were starting a 10-day campaign to focus on the melamine contamination.

Officers had also confiscated 300kg (660lb) of suspected chemicals, including 490 pounds of melamine, he said.

One suspect, surnamed Su, told police that from February 2007 to July 2008 he bought 200 20kg sacks of melamine, and sold them all to milk suppliers, Shi told a news conference.

Yang Chongyong, the deputy governor of Hebei province, where Sanlu is based, said the firm received customer complaints from March. But it was not until August 2 that it informed the city government of Shijiazhuang, the provincial capital. Officials there waited more than a month, until September 9, to inform their bosses in the provincial government.

The Hebei authorities took the problem to central government the following day. Sanlu finally ordered a recall.

Andrew Ferrier, the chief executive of Fonterra, which owns 43% of Sanlu, said it had urged disclosure "from day one".

The state news agency Xinhua reported that the mayor and four other city officials of Shijiazhuang had been fired. Sanlu's general manager, Tian Wenhua, was arrested. Four milk suppliers have been arrested and 22 detained.

China is the world's second largest market for infant formula. Ding Bing, the China coordinator for the World Alliance for Breastfeeding Action, said: "The milk powder companies do advertisements which exaggerate the effects of their products and make the mothers doubt [the quality of] their own milk."

• Additional research by Chen Shi