The incident happened in an area close to Khao Ang Rue Nai Wildlife Sanctuary. Chachoengsao is one of five provinces bordering the forest, along with Chonburi, Rayong, Chanthaburi and Sa Kaeo.
The herd of about 65 elephants included some 30 calves who crossed the road behind their mothers.
It is estimated that the population of elephants in the five provinces bordering the forest had increased as more than 90 per cent of elephants in the herd were female.