New Zealand authorities are investigating an Auckland-registered company's link to a cargo plane seized in Thailand with 35 tonnes of North Korea weapons onboard.

The hoard of explosives, rocket-propelled grenades, missile components and other armaments was discovered when the aircraft stopped to refuel in Bangkok's Don Muang Airport last week.

Its five crew members, from Kazakhstan and Belarus, have denied all knowledge of the weaponry and are being held in Bangkok.

The aircraft was recently leased to carry cargo by NZ-registered company SP Trading Ltd, which has offices listed in Auckland.

The Companies Office lists SP Trading Ltd's director as Lu Zhang, with an office in Queen St, central Auckland.

However, when the Herald called at the multi-storey office building, a woman who had worked there for more than a decade said she had never heard of SP Trading Ltd.

The company was registered at the Companies Office as having that address in July. Its sole shareholder is Vicam (Auckland) Ltd, and that company's shareholder is GT Group Ltd. While all three are registered to the Queen St address, none appear to be located there.

One director of Vicam (Auckland) lives in Auckland, but was overseas on business when the Herald phoned, according to a housemate.

PricewaterhouseCoopers director Alex Tan said New Zealand had a reputation as a "relatively easy place" to set up a shell company.

"A number of overseas people with less-than-honest intentions like to incorporate their company in New Zealand because it has a safe and clean and honest image," he said.

Mr Tan pointed to a recent report by the international Financial Action Task Force, which criticised parts of New Zealand's anti-money laundering regime.

"What it basically says is that anyone can set up a company in New Zealand as long as they have got one director and one shareholder," he said.

Mr Tan said there were a number of people who would set up a company in New Zealand for foreigners.

It was relatively easy to do as no proof of identity or residency details were required, he said.

Mr Tan said the new Anti Money Laundering and Countering Financing of Terrorism Act would put more onus on financial institutions to monitor their customers' legitimacy, but "current loose procedures" around setting up companies had not been dealt with.

Meanwhile, NZ police and the Ministry of Foreign Affairs and Trade are investigating the Kiwi connection to the cargo plane.

Police spokesman Grant Ogilvie said staff were "awaiting further information which will let us decide where to proceed from here".

According to the Wall Street Journal, the aircraft is managed by Georgia-registered carrier Air West Ltd. Officials in Kazakhstan and the Republic of Georgia said the carrier was recently leased by SP Trading Ltd.

Air West director Nodar Kakabadze said he had no information on the Kiwi company.

Previous owners had been documented by the United Nations as trafficking arms.

The ultimate destination of the plane remains a mystery, but military analysts said arms were probably destined for African rebel groups or a rogue regime, such as Myanmar.

Thai government spokesman Panitan Wattanayagorn said authorities were also investigating the Middle East as a possible destination, although the flight plan suggested it was headed to Sri Lanka.