Police and health authorities are investigating how four people, including a pregnant woman and a year-old infant, from a rural family died of poisoning at home in southwest China's Yunnan Province.

Xu Chaoping, a spokesman of the Luliang County government, said on Monday that an ambulance and doctors were called to the home at 7:14 p.m. Sunday, when the four showed symptoms of seizures and frothing at the mouth.

They were taken to the county hospital, where the three adults died at 7:50 p.m. Sunday and the child at 9:30 p.m., he said.

Xu said the dead had been identified as a 46-year-old local woman, Yuan Guixian, her pregnant daughter-in-law, Duan Hongyan, 22, her granddaughter, Feng Hangyu, aged 19 months, and fellow villager Wang Shilan, 46.

Yuan's son, who called the ambulance, had agreed to allow investigators to carry out autopsies, he said.

The son said he was called home by neighbors who found the family ill.

The county government had launched an investigation involving the police, and health, drug and food safety supervision departments.

Xu said the family had dinner at home. Rural families in the area usually had dinner at around 5:30 p.m, but it was not known what the family had for the meal.