Officials have warned the prime minister that submarine cables are "attractive espionage targets".

Europe and the United States are taking measures to safeguard fibreoptic and other cables from what NATO has called "seabed warfare", though a recent investigation found no evidence of foul play in the Baltic Sea.

Christopher Luxon said last month a "new threat has emerged" around cables that the government would look to manage as best it could.

An Official Information Act response shows five briefings to Luxon since July 2024 that touch on cable security, the most recent on 20 March, but nearly all the information is withheld on national security grounds - even the titles of the documents.

One briefing was summarised, saying "the vast amount of data that transits submarine cables makes them attractive espionage targets".

However, it added the leading risk was from accidental damage or natural disasters, noting the eruption of an undersea volcano in January 2022 severed Tonga's only subsea cable, impeding both its own and international relief efforts.

Luxon was also told, "Disruptions to these services caused by damage to submarine cables can be highly detrimental" and, "Submarine cables can also be damaged during conflict"; all the accompanying advice was withheld.

Maritime New Zealand's guidance on cables stresses the law prohibiting fishing and anchoring in certain zones that could damage them, but nothing in the guidance online allows for deliberate sabotage or espionage.

Defence and Customs have just bought two marine drones that can patrol the coast for long periods, though their focus is drug smuggling, according to the government.

Cables were damaged in the Baltic Sea last year, amid a series of cable or pipe outages, and authorities voiced fears a Chinese ship dragged its anchor over them deliberately.

While an investigation was inconclusive, the NATO military alliance has put more frigates, aircraft and naval drones into the area.

The US has made recent moves to restrict China's laying cables and begun a review to tighten up the two-decade-old rules on subsea cables.

However, the way the largely private industry of subsea development and operation is set up currently gives the government little national security leverage, at a time when AI and datacentres are fuelling an explosion in data transfer.

The review by the Federal Communications Commission has proposed measures such as requiring companies that want to 'land' a cable to show a certified cybersecurity risk management plan, and setting up a new coordinating forum.

Yet the US did not include subsea cables as a standalone sector when it updated its critical infrastructure framework last year.

US commentators are now warning that cable sabotage will inevitably spread to the Middle East, that the vast majority of US military strategic communications is by the cables - and that most are in relatively shallow water of less than 400m, with their locations publicly available. There are calls for Washington to begin building partnerships to protect them.

New Zealand set up a new risk and resilience framework in December 2024; while it mentions critical infrastructure, subsea cables do not feature in the publicly-available official commentary on national security.

The new risk framework puts the Transport Ministry in charge of any big maritime security incident.

The country has laws that restrict marine activity around cable landing zones, such as at Takapuna. A ban on fishing or lowering anchors in a swathe of Cook Strait is monitored 24/7 by a cable patrol vessel. The country has also spent millions alongside Australia on expanding data cable access for Pacific islands.

"Cable and pipeline owners, such as Transpower, Spark and Southern Cross Cables, spend millions of dollars each year to protect the submarine cables and pipelines," said 2021 guidance from Maritime NZ.

"Any damage could take months to repair."