Officials say they are questioning nearly 80 people suspected of involvement in the latest scandal. On Monday, the police arrested two brothers who ran a milk collection center in Hebei Province suspected of adding melamine to diluted milk, according to the official news agency Xinhua. Adding the chemical makes the material test at higher concentrations of protein.

Fonterra, the New Zealand conglomerate that owns a 43 percent share in Sanlu, said it first learned last month that the Chinese company was selling contaminated powder. On Monday, New Zealand officials blamed local Chinese officials for failing to take action until the New Zealand government contacted the central authorities in Beijing.

Image Babies who had been fed Sanlu milk powder were checked on Sunday at a hospital in Nanjing. Credit... Agence France-Presse — Getty Images

The prime minister of New Zealand, Helen Clark, said Fonterra officials had been “trying for weeks to get official recall, and the local authorities in China would not do it.”

“I think the first inclination was to try and put a towel over it and deal with it without an official recall,” she said, according to Television New Zealand, a government network.

Chinese health officials said physicians had examined 10,000 infants who had been fed the Sanlu formula and found that 1,253 had been sickened. Ma Shaowei, a vice health minister, said many of the ailing children were from poorer areas, according to a transcript on the Internet. But at least three babies were hospitalized as far away as Hainan, the island province not far from Vietnam.

It seems likely that contaminated formula had been distributed for several months.

The two deaths attributed to the bad formula, both in Gansu, occurred long before the scandal became public. One was a 5-month-old boy who died on May 1; the other was an 8-month-old girl who died on July 22, according to the Health Ministry.