A search is underway for a four-year-old boy who has been missing from a family homestead in South Australia's mid-north since last night.

The boy was last seen at his home, about 40 kilometres south of Yunta, which is about 200km east of Port Augusta, at around 5pm.

A police helicopter assisted in the search last night using an infra-red camera, but did not locate the boy.

"Police and PolAir recommenced the search at first light this morning and a drone was also utilised to cover a greater search area," a statement said.

"Water Operations police will head to the area tomorrow morning to conduct a search of dams and tanks on the property."

SA Police say the boy is Caucasian with long blonde curly hair, and he was wearing a grey sun hat, a cobalt blue long-sleeve T-shirt with a yellow

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