New Zealand spies were unable to obtain video surveillance warrants for six months last year due to a loophole that subjected the nation, and possibly Australia, to a period of vulnerability to terrorism.

Documents obtained by the NZ Herald revealed the NZ Security Intelligence Service was unable to use video surveillance tools to watch terrorism suspects in their cars, homes or workplaces between April 1 and September 28 in 2017.

NZSIS director-general of security Rebecca Kitteridge told the former minister in charge of NZSIS Chris Finlayson about the gap in the law in a briefing with the minister on June 30, 2017.

The gap extended from when old legislation expired until new legislation came into effect.

Mr Finlayson refused to seek a legislative solution to remedy the loophole, noting on a document, “don’t even bother asking”.

The former minister in charge of the top spy agency placed the blame squarely on the NZSIS when asked would have been to blame had there been a terrorist attack during that time.

“They would have been”, he replied, referring to the NZSIS.

New Zealand Prime Minister Jacinda Ardern said there had been a drafting error in the legislation, but added “obviously that’s been resolved,” Ms Ardern told reporters.

The revelations of potential security risks follow Home Affairs and Immigration Minister Peter Dutton saying New Zealand is being “marketed and pitched” as a “backdoor” for asylum-seekers headed to Australia.

Currently New Zealand citizens can visit, study, stay and work in Australian on temporary, but indefinite, subclass 444 visas.

“The fact is that [people smugglers] are marketing New Zealand, people are believing New Zealand because they’ve heard Bill Shorten talk about New Zealand, and we need to call him out,” Mr Dutton told journalist Miranda Devine on radio.

“People smugglers are out there marketing at the moment saying there will be a change of government in Australia, pay your money and you’ll get to Australia under a Labor government,” Mr Dutton said.

The comments follow Malaysian authorities intercepting a tanker carrying 131 Sri Lankans bound for Australia or New Zealand this month.

Mr Dutton also told the Miranda Live radio program that a move to send arrivals by boat to New Zealand was “essentially like saying we’ll just send people to Sydney or Melbourne because people know New Zealand is a back doorway into our country.”

“Labor doesn’t get this yet, but it’s the case that New Zealand is the only country in the world you can hop on a plane, and come to Australia and get a visa on arrival,” he said.