Police say they've rejected two attempts to import into New Zealand a gun accessory drawing attention following the largest mass shooting in United States' history.

"Bump stocks" have become a focus of gun control discussions in the US after gunman Stephen Paddock used them when he killed at least 58 people and injured about 500 at a music concert in Las Vegas this week.

Attached onto guns, the devices effectively allow some semi-automatic weapons to fire at rates resembling fully automatics, making them significantly more dangerous.

Under New Zealand law, a special permit is required to import the accessory.

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Police on Friday confirmed that two permits had been requested to import bump stocks into New Zealand in past years.

Police were unable to be more specific on when exactly this occurred, but said both were declined.

"A bump fire stock importation would require the importer to provide police with a special reason for the importation," a spokeswoman said.

She said police were also aware that "some years ago" Customs had intercepted a bump fire stock coming into New Zealand."

Christchurch gun dealer David Tipple told NZ Newswire this sort of hardware is not available in New Zealand.

"It's the worst thing you can have for a gun [but] it's not an issue here," he said.

"I've never seen one before in this country."

New Zealand has a relatively high rate of gun ownership by global standards, with more than 1.3 million guns - nearly 30 per 100 people - believed to be in the country.