A routine dagga-spraying operation went horribly wrong when a police helicopter crashed on to a sports field, seriously injuring the pilot in the Midlands town of Weenen in KwaZulu-Natal on Tuesday.

The accident happened about 7am when the pilot, named only as a Senior Superintendent De Waal, came in for refuelling at the South African Police Service base next to the sports field after spraying dagga crops in the area.

As the helicopter was descending, it hit a lamp pole, tilted and crashed to the ground, said police Senior Superintendent Henry Budhram.

The helicopter did not catch alight.

The solo pilot sustained neck and back injuries and was airlifted to a hospital in Pietermaritzburg.

No one on the ground was injured.

Weenen SAPS station commissioner Captain Len de Lange said the helicopter was extensively damaged.

The Civil Aviation Authority and the SAPS are expected to investigate the cause of the crash.