A four-year-old boy is in critical condition after an incident at a swimming pool.

Police and ambulance attended the incident at Sockburn - about 10km from Christchurch - about 2.30pm.

A spokesman for Christchurch Hospital said the boy is in critical condition but details of his injuries could not released without permission from the boy's parents.

A St John Ambulance spokesman earlier described the boy's injuries as "serious" but did not have specific details either.

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"We sent a rapid response and an ambulance to the scene which was an address on Main South Rd, Sockburn," he said.

"We have transported one patient, male, aged under five years, to Christchurch Hospital emergency department in a serious condition. We don't have specifics about his injuries."