Potentially deadly substances which mimic ecstasy are being leaked through New Zealand borders in "plain sight".



Since Customs launched Operation Static in February, there has been a concerning increase in the amount of psychoactive substances intercepted.



"Customs is intercepting up to 15 suspected psychoactive substances each week, mostly through mail and air freight," said Mark Day, customs manager investigations.



He added that a 1kg package of a psychoactive substance could yield up to 10,000 pills. However, opportunist drug suppliers add other illegal agents to the to bulk up their product in order to make up to 30,000 pills.



The pills sell between $20 and $40 on the street as ecstasy mimics.



Day said the purity level of the pills was "very low" which could see users take a few of them during the course of a night.



"As a nation, we are yet to see thee health issues that come out of these drugs," said Day.



"We need to stop the demand and the culture in our society where is it readily acceptable to take these pills."



In the past few days, four people have been arrested and Customs officers have visited more than 40 homes in Auckland, Wellington and Christchurch in relation to suspicious packages.



At least 100 investigations are being carried out at the moment.