A further half a dozen primary, intermediate and high schools have gone into lockdown this morning as threatening emails received by the institutions are being monitored by police - and it follows a concerning trend according to a police expert.

Auckland’s Murray Bay Intermediate School is one of many schools that have chosen to close due to the threats, with police confirming that organisations are again today being targeted by concerning emails.

The same incidents occurred yesterday, where kindergartens were evacuated and hospitals were put on alert.

According to Chris Cahill, president of the Police Association, the threats used to be taken with "a bit of lightness" but noted the world has changed dramatically in recent years.

"In New Zealand, it changed in 2019," he told The Mike Hosking Breakfast, referring to the Christchurch Mosque shootings.

"So, there's got to be a thorough threat assessment done on these things."

Cahill wouldn't reveal the specific techniques that officers use to determine whether a threat is a hoax or not but did confirm there were ways officers would work out if an email had the hallmarks of something more serious.

According to the association president, threatening emails have tended to become more common at the end of the calendar year.

"We do seem to get a lot of these around exam time, university exam time," he said.

"It tends to increase so that's what we're aware of, but sometimes when you get multiple threats to different institutions it's probably something you go 'mmm, maybe'."

Hosking asked what the process looked like when it came to tracking the people who sent the threats, Cahill said it can be a difficult mission to accomplish.

It would depend on how motivated and clever the offender was, but police have increased their skills in the online space, through the cybercrime unit, to crack down on online threats.

"We know it's taken some time because you use overseas servers and you route things out in different ways, but we've got some good partnerships overseas," he said.

"I think I'd be worried if I was the person who sent it."

In July last year, six North Island schools were either thrust into lockdown or evacuated following threats made towards the schools over the phone.

The hoax bomb threats were made to 18 schools across New Zealand and were believed to be computer-generated phone calls threatening harm to those in the school.