Letters sent to Hokitika have been disappearing due to two wayward posties.

Two West Coast posties have been fired for not delivering mail.

A New Zealand Post (NZP) spokeswoman said an internal investigation had found some items of mail that a contractor in Hokitika was responsible for had not been delivered in "recent weeks".

It is understood at least some of the undelivered mail had been destroyed.

Not delivering mail is an offence under the Postal Services Act 1998.

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Town resident Kath Rogers thought something was odd when she received a fraction of the mail she normally received over a three-week period, during which she spent two weeks on holiday in Australia. She said she was then dumped with 18 letters on a weekend afternoon, but only after complaining.

"When I got home there was one letter. It was from NZP saying my mail would be delivered to her (Rogers' sister) house.

"When I got home she handed me about six letters. I said 'That doesn't look right. I usually get a lot of mail'."

Once she had returned home Rogers said she received nothing for nine days except one letter that didn't belong to her. She then rang NZP a number of times trying to get an answer.

Rogers said she suddenly received 18 letters on a Saturday afternoon – a time when she did not normally receive mail.

"Where it had been is what I'd like to know. My credit card thing said it needed to be paid by February 28 and I got it on March 13.

"Another person rang me who didn't want to be named and said 'I've seen bags and bags of it (mail) being thrown out'.

"God knows where all this mail is."

The NZP spokeswoman said the company "sincerely apologises for the concern and distress this may have caused" and that the mail was "unrecoverable".

"We always hold our contractors accountable. The subcontractors who were responsible are no longer delivering mail and the situation is being managed in accordance with our investigation processes."

Normal mail delivery had resumed, she said.

"We would like to reassure residents of Hokitika that we take mail security seriously. We believe this was an isolated incident."

Postal Workers Union southern region president John Maynard said the incident was a direct example of the "weaknesses" associated with NZP employing contractors.

"We've said all the time to the company 'You're losing the integrity of the mail when you start contracting out because they are no longer direct employees of the company'."

He said this particular business model was increasing the likelihood of these sort of incidents because the delivery network was moving further away from the company.

"NZP used to have a very highly respected, very efficient postal system and as a union we've been concerned for quite some time about decisions being made by the company that we think reflect negatively on the integrity of the system."

Maynard said the union would work with NZP to ensure the postal network became more efficient.