A chef's mistake of adding pesticide instead of a sauce while cooking has left one person dead and two others in critical condition in north China's Inner Mongolia Autonomous Region.

Police in Baotou City told Xinhua on Thursday that the chef was among the 21 people who fell ill after eating lunch at the construction site of the Beijing-Tibet Expressway expansion project in Baotou on Tuesday.

The pesticide, identified as carbofuran, was found in samples of the food.

Police said evidence shows that the case was a crime of negligence.

The workers are all migrant workers employed by the project contractor, the Inner Mongolia Highway Engineering Co.