Image copyright Avsec Image caption The 10-month-old mixed breed was a trainee sniffer dog

A security sniffer dog that escaped from its lead and grounded flights at Auckland airport has been shot dead by police, triggering fury in New Zealand.

Authorities said the dog, called Grizz, could not be captured after it ran off. The incident grounded 16 flights and caused delays for several hours.

An airport official said the decision to shoot the dog was a last resort.

But it has been met with outrage, with many asking why the dog could not have been tranquilised instead.

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Grizz was a 10-month-old trainee sniffer dog at Auckland Airport handled by the government's Aviation Security Service (Avsec).

Avsec spokesman Mike Richards said that around 04:30 local time (15:30 GMT Thursday) Grizz was getting into a dog unit wagon parked in the airport's public landside area, when "something" caused it to escape.

At that point a gate connected to airside, or security area, had been opened to let a truck through. Grizz managed to run through the gate on to the tarmac.

'Exhausted every option'

Mr Richards said a "massive effort" was launched to locate the dog in pitch black conditions, and for the first two hours Grizz could not be found.

When it was finally located, "he would not let anyone near him and kept sprinting across runways.

"We tried everything: food, toys, other dogs, but nothing would work," said Mr Richards, adding that the area was "too vast and too open" to erect temporary fencing.

Airport officials finally ordered police to shoot Grizz.

"We exhausted every option available and could not catch it," an Auckland Airport spokesman told the BBC.

When asked why the dog could not be tranquilised, the spokesman said: "I do not have the answer to that. But there were no tranquiliser guns at the airport, and the police do not have them either."

She said tranquilisation would be part of an incident review undertaken by Avsec.

Image copyright Facebook / Auckland Airport Image caption The incident has prompted a deluge of angry comments on the airport's Facebook page

New Zealand animal rights organisation Safe said it was "appalled about the needless killing of this dog".

"A tranquilliser gun should have been used after efforts to catch the dog failed. If such a gun was not available - which it should - then they could have borrowed one from Auckland Zoo or elsewhere," a spokesman was quoted as saying by the New Zealand Herald.

The incident has prompted a deluge of angry comments on the airport's Facebook page.

But Callum Irvine, head of vet services at the New Zealand Veterinary Association, told New Zealand's Stuff website that tranquilising an animal was complex.

"There just isn't ready access to tranquiliser guns and darts in New Zealand, and even if authorities did manage to get their hands on one in time, there are so many other factors to take into consideration, like how close the animal is, the animal's weight, age and how much adrenaline was also running through the body."

He said tranquilising an animal on the loose could be very difficult.

"If it's not done right, a partially sedated animal can become even more distressed, and fearful and difficult to manage - and become even more of a danger to those around it."