Police in Xi'an, capital of Shaanxi province, have detained two people suspected of using formaldehyde to make noodles.

Police said the provincial Public Security Department received a report from residents on May 20 that a vegetable market in the city's Lianhu district was making noodles with suspicious substances. Lianhu police began an investigation in the market that day.

Meng Jiangwei, an officer at the Lianhu district Laodong Nanlu police station, said they found two noodle-making shops in the market that used formaldehyde as an ingredient.

Police detained the shop owners and seized two bottles of formaldehyde and more than 300 kg of formaldehyde-poisoned noodles.

Police said the shop owners, surnamed Zhang and Tang, confessed to making noodles with formaldehyde to keep them fresh in the hot summer days.

Formaldehyde is a highly toxic substance that the World Health Organization says can cause cancer and birth defects.

Zhang and Tang are still being held, and the investigation is ongoing.

In recent months the central government has stressed the need to ensure food safety, and a number of criminal cases have been reported by the Ministry of Public Security and Supreme People's Court.

On April 7, the State Council ordered all localities and departments to continue their crackdown on the illegal use of food additives.

On May 2, the Ministry of Public Security announced five cases of crimes concerning meat that police across the country had discovered, and on May 3, the Supreme People's Court announced a number of criminal cases on food safety, including producing and selling fake liquor, selling sausage and ribs made from pigs that had died, and the production and sale of gutter oil.