WELLINGTON (AFP) - New Zealand police said four officers were shot on Wednesday (March 9) during a siege at a rural property that began when an offender started taking potshots at an aircraft being used in an anti-drug operation.

One officer was serious but stable and the injuries sustained by the other three were not life threatening, Deputy Commissioner Mike Clement said.

He said the siege, which was still ongoing at 6pm local time, began after a police plane searching for cannabis came under fire near the remote North Island town of Kawerau.

The Armed Offenders Squad (AOS) was deployed and four of its officers were shot in a stand-off at a rural property.

"It is always distressing for us all when officers are injured doing their duty," he told reporters in Wellington.

Mr Clement said no one was injured aboard the plane that came under fire, adding that indications pointed to a lone offender, but he was unable to go into too much detail.

"I simply can't, it's an investigation that's ongoing," he said. "He might indeed be watching us now on his own television."

Regular police in New Zealand do not carry firearms, relying on the specialist AOS.

The country tightened its gun laws to restrict access to semi-automatic rifles in 1992, two years after a mentally disturbed man shot dead 13 people in the South Island town of Aramoana.

However, anyone over 16 can apply for a standard firearms licence after doing a safety course, which allows them to purchase and use a shotgun unsupervised.