Two children died in northern China after drinking yoghurt which a disgruntled kindergarten owner had injected with rat poison, state media reported on Thursday.

The two girls in Hebei province drank the tainted yoghurt after their grandmother found it by a roadside, Xinhua news agency said.

The children, whose ages were not given, were found "foaming at the mouth," shortly afterwards, the report said. One died before reaching hospital while the other died on Wednesday.

A preliminary investigation found that the yoghurt had been adulterated with rat poison by a female kindergarten owner competing for village students with the owner of a rival establishment, the agency quoted local police as saying.

It said the woman had asked a man to place the poisoned yoghurt on the roadside along with several notebooks. It was unclear from the report how the poisoning would have discredited the rival kindergarten.

Many children in the countryside are cared for by their grandparents because their parents have migrated to cities to find work.