Funding for the police's Special Tactics Group had increased nearly thirty-fold since terrorism became more prevalent in the early 2000s.

Police spending on its dedicated tactical group has increased nearly 30-fold since the World Trade Center terrorist attacks in 2001, with Kiwi taxpayers now funding them to the tune of $6.2 million.

Information released under the Official Information Act shows that annual funding for the Special Tactics Group (STG) was just $226,000 back in 1999-2000 and has grown to reach $6.26m in 2017-18.

In 2007-08 spending on the group was more than $5.4m. Funding has consistently been more than $6m since 2014-15.

The unit is used by police to respond to "high-end tactical incidents" beyond the capabilities of the Armed Offenders Squad (AOS). Their jurisdiction includes terrorism and hostage rescue.

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NZ POLICE/SUPPLIED Special Tactics Group members breach a door in training.

High profile incidents involving the STG include the 1990 Aramoana massacre, the Napier seige in 2009 and the response to gunman Quinn Patterson in Northland last year.

They have also been deployed overseas to assist with security operations at APEC and G20 summits in Australia.

Inspector Geoff Jago, police operations support commander, said the funding increase could be attributed to the STG becoming a full-time unit "around" 2002.

The unit was initially raised the 1970s as the Anti-Terrorist Squad and was staffed with part-time members before changing its name in the 1990s, Jago said.

It became a fulltime unit following the increase in international terrorist incidents in the early 2000s, such as the September 11 attacks in the United States.

NZ POLICE/SUPPLIED STG training with a police dog across tussock covered country.

"It certainly would have been based on international events. New Zealand wanted to ensure it had a full-time capability able to [respond to such events]."

The STG provided a capability to deal with terrorism, barricaded offenders, hostage rescues, high-risk covert surveillance and VIP security, Jago said.

"STG is a full-time unit, whereas AOS are part-time – with all AOS [officers] undertaking other policing duties. [The STG] have specific training in certain tactical options and for more prolonged or hostile operations."

Bush-craft, rappelling, building entry and "room clearance" were all techniques used by the STG that were outside of usual police training.

Dr John Battersby, fellow at the Centre for Defence and Security Studies at Massey University, said it was prudent for the police to maintain the STG.

NZ POLICE/SUPPLIED STG members rappel from an air force helicopter.

New Zealand could see what was happening overseas and could not afford to wait until it was struck by terrorism, he said.

Modern acts of terrorism generally happened quickly and the police needed a unit with their specialist skills and capabilities as they were the first organisation to respond to such incidents.

"Terrorism is a criminal act, especially the type of terrorism we are seeing now where people commit a succession of criminal offences or go after a volume of a country's citizens," Battersby said.

"Apprehension is a police duty. Almost all police organisations around the world retain a similar capability for this reason."

In the 2017-18 financial year the STG were deployed 84 times. Part-way through December, the AOS had been deployed 961 times in 2018.

NZ POLICE/SUPPLIED STG receive training in areas outside of normal policing skill sets including bush-craft.

Jago did not consider the STG an elite force, but rather, a specialised section available for use by police when and if needed.

They trained with equivalent Australian units and elements of the New Zealand Special Air Service (SAS). D Squadron of SAS is the Defence Force's domestic counter-terrorism unit.

STG units are located in Auckland, Wellington and Christchurch. Members are recruited from the the AOS and are required to pass selection and qualification courses.

Jago would not say how many officers were assigned to STG units.