Health officials in China are investigating a brand of baby formula after 14 infants were treated in hospital for kidney stones.

The infants are all under 11 months and shared symptoms such as vomiting, the Xinhua news agency reported. They are from a rural area in northwest Gansu province.

"It is rare for babies to get kidney stones, let alone so many babies at the same time," Zhang Wei, a doctor at the Gansu-based No.1 Hospital of the People's Liberation Army, who treated the babies, was quoted as saying.

The babies all drank the same brand of cheap milk powder, identified as the "Sanlu" brand, the report said.

Sanlu, a Chinese dairy company, said its brand was used illegally and it has sent teams to investigate, the news agency said.

Provincial health officials are also investigating the powder to see if it is connected to the kidney stones – masses of salts or minerals that crystallize in the kidney. If the stones become large enough to stop the flow or urine from the kidney, they need to be removed surgically or by other methods.

In 2004, at least 13 babies in China's eastern Anhui province died after they drank fake formula that investigators said had no nutritional value. The deaths prompted food and health investigations and international concern.