More than three tonnes of illegal drugs were seized at New Zealand's border last year. 

The seizures mean that an estimated $1.4 billion of potential social harm from methamphetamine was prevented, Customs New Zealand says.

Around 2600 seizures were made at the border throughout 2019. Another 437 kilograms of drugs were seized offshore by international border partners before they could reach the country. 

More than a tonne of methamphetamine was seized as well as almost 800 kilograms of MDMA.

Customs Minister Jenny Salesa says the increase in drug trafficking is due to Australian deportees.

"We are experiencing an evolution in the volume and craftiness of the criminal syndicates who seek to peddle these products in our communities," she said.

While acknowledging the sale of drugs is a global issue, she said Australian deportees are part of the problem. 

"This is partly due to the criminals who have returned from Australia as deportees, and have brought their know-how and international criminal networks."

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According to Salesa, funds from the 2018 Budget to boost Customs resourcing are behind the record haul.

"We have given Customs the cash injection they needed to boost their capabilities, plus disrupt more criminal networks offshore to stop illegal drugs before they even leave the export country," she said in a statement on Monday.

The focus on stopping supply is a key part of the Government's health-based approach to social issues liked drug abuse.

"[The] Government is putting more resources into addiction, detoxification and residential care services for New Zealanders who are struggling with drug and alcohol issues," said Salesa.