UPDATED 5.30PM: New Zealand women as well as men are travelling to Syria to join the Islamic State, a top spy boss says. 

Director of the Security Intelligence Service Rebecca Kitteridge has revealed the fact at annual review hearings at Parliament this afternoon.

LISTEN TO STRATEGIC ANALYST PAUL BUCHANAN WITH LARRY WILLIAMS ABOVE

There are already "thirty to forty" New Zealanders being monitored by the intelligence services. Prime Minister John Key revealed earlier this month that some were under surveillance 24-hours a day. 

Kitteridge noted today that New Zealand women leaving for Syria was a development that they've only learnt about over the last year.

Kitteridge said presumably they're wives or partners of those fighting, but it's difficult to see what they do when they go.

"We definitely have intelligence that they went," she said. "Whether they are going to fight or whether they are going to support other fighters is not clear but it's a real concern that they would go at all."

Kitteridge said they were people who have other problems in their lives, not your average type of person who goes to work, is happily married and raising kids.

"I would say there's a sort of pattern of people who seem kind of disengaged in some way with a kind of productive life."

"[There's a] range of ages, range of backgrounds, no particular pattern there."

The SIS director also pointed out that the threat to New Zealand's domestic security posed by 'foreign fighters' and other extremists is real, and continues to develop.

She says the number of New Zealanders fighting alongside ISIS remains small but has increased.

"Individuals who succeed in travelling to the Middle East to support I.S. [Islamic State] will be exposed to acts of barbarism and maybe trained in combat."

"They pose a significant threat if they return to New Zealand or travel to other countries."

However strategic analyst Paul Buchanan said New Zealanders shouldn't be too concerned about them returning because "it's pretty well known that less than fifty percent of the foreign fighters and the brides who go to the Middle East come back alive from that venture."

Kitteridge was also questioned at the hearing today as to why the Inspector General of Intelligence and Security wasn't formally notified of two visual surveillance warrants as required by law.

She insisted it was an oversight, it should not have happened, and she was "making some internal inquiries about how that could have happened."

"In the meantime there have been changes to the processes to ensure that won't happen again.

"I've given my apology to the Minister because it should never have happened at all."