A helicopter that crashed northwest of Whanganui, killing one person, was being used to spray farm land.

Emergency services were called to the scene inland from Kai Iwi, at Brunswick, about 9.30am.

The male pilot of the helicopter died at the scene, Police said. He was the sole occupant.

A local farmer, who had worked with the pilot many times, said the man was very experienced and had worked in the area for many years.

"As a local farmer it's just a bit close to home," he said.

"Everyone goes up with him, shows them where they want sprayed and then he drops you off and he goes and does his thing.

"He was very, very experienced."

The farmer said it would be a huge loss for the farming community in the area. "He was a great fella, it's a massive loss."

The helicopter was carrying out routine spraying of farm land before the crash, Police said.

The helicopter crashed on rural Koatanui Rd and was spilling fuel when emergency services arrived, police central communications Inspector Dave Rose said.

Police cordoned off the scene from Currie Rd while the police serious crash team from Palmerston North investigated the wreckage.

The main part of what is believed to be a Hughes 500 helicopter is on a dead-end section of Koatanui Rd. Pieces of the tail lie in a nearby paddock.

The Civil Aviation Authority has been informed of the crash.