New Zealand police have confirmed the Manchester terror attack which killed 22 people triggered security and risk be re-evaluated to ensure the safety of the British & Irish Lions and their 22,000 touring fans.

The May 23 (NZT) tragedy - which saw a suicide bomber detonate a shrapnel-laden homemade bomb in the foyer of Manchester Arena as children exited an Ariana Grande pop concert - came four days before the massive Lions contingent landed in Auckland for their high-profile tour.

The attack threw months of planning into urgent review as police and security experts swung into action to reassess whether their strategies were sufficient to guard against a potential attack on New Zealand soil.

Police refused to reveal tactics, equipment, staffing numbers and other specific details of security measures for "obvious reasons". But they have confirmed "extensive plans and resources" as well as a specific response to the Manchester terror attack.

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"We have extensive plans and resources in place to deal with a raft of potential contingencies, which involves anticipating all events and risks which could impact on the series, both natural and man-made," a police spokesman said.

"This includes consideration of the tragic events in Manchester and other incidents like it to help inform our planning."

Kiwi agencies are also in contact with foreign police in their bid to keep the Lions tour safe.

"We also continue to liaise and share information with our international partners, including overseas law enforcement agencies," the spokesman said.

"We can reassure the public and our visitors that we are well resourced and supported to safely manage this event, working in conjunction with our other partners."

Former Prime Minister Sir John Key revealed two years ago that 40 people on a watchlist were linked to, or "on the periphery" of the Islamic State (ISIL) and were likely to be regularly reading the extremist group's propaganda.

Key said one or two New Zealanders on a terror watchlist were considered so threatening that were subject to monitoring every minute of the day.

The New Zealand Security Intelligence Service (NZSIS) said the number on the "counter terrorism risk register" remains around 40.

"A number of agencies in New Zealand including NZ Police and NZSIS have responsibility for maintaining New Zealand's security, as well as identifying and advising around risks to national security," a spokeswoman said.

"In the 2015/2016 year the NZSIS reported that there were between 30-40 people on the counter terrorism risk register.

These individuals were assessed as representing an actual or potential threat to New Zealand related to terrorism, which could include foreign terrorist fighters or individuals providing financial or facilitation support."

New Zealand security researcher Dr Bridgette Sullivan-Taylor said the risk of a terror attack on New Zealand soil was low - including a lone wolf attack such as the 2014 hostage crisis at Sydney's Lindt Cafe which saw two hostages die.

Sullivan-Taylor, who reviewed the UK's national security and Civil Contingencies Act for then-Prime Minister Tony Blair, said the role of the internet in radicalisation was still a concern.

"I'd say the risk is probably pretty low," Sullivan-Taylor said. "But their hotspots of radicalisation seem to be developing through the internet so I'm sure the Australian and New Zealand governments are monitoring activity on the internet.

"I imagine they're sharing a load of information trying to monitor homegrown radicalisation, for whatever motive."

Sullivan-Taylor said hosting the Lions tour would help lift New Zealand security standards in general.

"The Lions tour exposes New Zealand organisations to international best practice," she said.

"So to be eligible for this tour and future celebrity concerts and insurance liabilities, it will presumably require meeting standard a which will be constantly reviewed and assessed based on country of origin - such as the UK or USA."