Wellington, Jan 18 (IANS): New Zealand is under low level of terrorism threat, which means a terrorist attack remains "a realistic possibility", a report said on Thursday.

The report is based on an assessment at a point in time by the multi-agency Combined Threat Assessment Group (CTAG), which is based on a range of classified and open source material, reports Xinhua news agency.

Maintaining the threat level at low reflects the fact that CTAG has not sighted information to indicate New Zealand is currently the target of credible and specific attack plans by violent extremist groups or individuals, either based in New Zealand or offshore, the report said.

New Zealand Security Intelligence Service (NZSIS) Director-General of Security Andrew Hampton made the determination following a routine annual review.

"The purpose of the National Terrorism Threat Level is to inform relevant government agencies about the likelihood of a terrorist attack in New Zealand," Hampton said.

New Zealanders should remain alert to signs of violent extremism and report behaviors and activities they find concerning, Hampton said.

The threat level and the assessment that underpins it allow relevant government agencies to ensure that they are appropriately placed to mitigate any risks, he said.

While the setting remains at low, it is important to remember it does not mean there is a complete absence of threat, he added.

"An attack remains a realistic possibility and there are individuals of concern being investigated by the NZSIS," Hampton said.

The National Terrorism Threat Level is continually evaluated and could change at any time, he said.

A terrorist attack happened on March 15, 2019 when a gunman attacked two mosques in Christchurch, the largest city of New Zealand's South Island, resulting in the death of 51 worshippers.

The day was described as New Zealand's darkest day.