Proposed law changes to respond to the threat of Islamic State supporters will not lead to inappropriate surveillance by the SIS, the Defence Minister says.

The Government plans to change the law to allow the Minister of Internal Affairs to cancel passports for between one and three years and temporarily suspend them for 10 days in urgent cases.

It will also allow the Security Intelligence Service (SIS) to carry out video surveillance on private properties in cases of security concern.

In emergencies they will be allowed to begin surveillance up to 48 hours before the issue of a warrant, with the approval of its director.

Civil rights lawyer Michael Bott said the changes were disproportionate to the actual threat level and would erode personal freedoms.

"If these people are to be monitored now then why do we have to ... give the state more power to intrude on our lives. The changes have to be proportionate and at this stage we haven't seen the evidence," he told Morning Report.

Defence Minister Gerry Brownlee said security agencies need to be able to monitor the threat.

"What would New Zealanders think of agencies of the state knew about people who had expressed some of the intentions that these people have but then did nothing and an incident occurred."

Photo: RNZ / Diego Opatowski

Intelligence agencies would not be able to go on a 'fishing expedition' for information because they have to ensure any evidence gathered is admissible in court should any charges be laid, said Mr Brownlee.

"If they want to be able to collect information speedily for the use in a prosecution then they're going to have to be very very certain that had normal processes been followed, they would be able to get a warrant."

Labour and New Zealand First have indicated they are likely to support the law changes, but the Greens say they are an erosion of human rights.

Yesterday Mr Key revealed up to 40 people were on a Government watchlist because of their involvement with or support for Islamic State and another 30 to 40 required further investigation. Five New Zealand citizens or residents are fighting for IS in Syria, and nine New Zealanders have had their passports cancelled for wanting to do so.

Mr Key said the proposed changes would be subject to a sunset clause, but the proposed new legislation has raised concerns among academics.

Nigel Parsons, senior lecturer in the politics programme at Massey University, said it was easy to overstate the risks being posed to New Zealand.

"Once civil liberties are gone, once powers of surveillance are increased, those powers are typically difficult to roll back and those liberties are difficult to reclaim," he said.

Robert Ayson, professor of strategic studies at Victoria University, said there was a threat to New Zealand, but questioned whether it was being painted as more than it really was.

"When you are talking about video surveillance before a warrant has been granted that starts to test whether we are willing to sacrifice our democratic values in order safeguard them."

He said the Government needed to stick to its promise of a sunset clause when introducing the new laws.

"Because Islamic State aren't going to be here forever, any emergency powers that are granted should be removed as quickly as they possibly can be as the situation changes," he said.

New Zealand Federation of Islamic Associations vice-president Javed Khan was alarmed by the threat outlined by the prime minister.

He said he was aware of five to 10 people associated with Islamic State - not the 80 or so mentioned by John Key.

"We would like know or identify who these people are in the community. We don't have that information," he said.

"We would like to assist the government agencies to address this issue, so that the country remains peaceful and safe for everybody."

Mr Khan also warned against the surveillance measures, saying innocent people's rights could potentially be trampled upon.

Photo: AFP

Some Wellingtonians supported the proposed new laws - to a degree.

A web developer, Gareth Bradley said he did worry about the threat to the country, but is divided over new surveillance powers.

"I really dislike mass surveillance, however when it's phrased in terms of something like there is a clear association with ISIS, it seems like I'd give it the green light."

An accountant, Andrew Flanagan, said he believed the risk of a terrorist threat was very low, but New Zealand should still have its guard up.

"It's naive not to have those measures, because the threat is there, but personally it doesn't really concern me all that much - it doesn't keep me awake at night."

Mr Flanagan said there were bigger risks in life than a terrorist attack in New Zealand such as a car crash or being mugged.