A massive $50 million consignment of methamphetamine has been seized in Christchurch and two men arrested in what is largest-ever seizure of methamphetamine in the South Island.

The drugs arrived into Christchurch in an airfreight consignment sent from Mexico on November 1, police say.

Detailed examination found 49kg of methamphetamine concealed within a shipment of safety lights.

It consisted of 40 separate packages of around 1-1.2kg each, which has yet to be further forensically examined to determine the exact weight of the product.

Police say the drugs had a potential street value of $50m, and the seizure has prevented $60.71m of "additional community harm".

Search warrants were executed at a number of addresses in Christchurch and in Auckland after a two-week joint police and Customs operation.

Two Christchurch men, aged 25 and 31, have been arrested and appeared at Christchurch District Court today on charges of importing a Class A drug, and possession of methamphetamine for supply.

They have both been remanded in custody to reappear in Christchurch on November 20.

Detective Inspector Corrie Parnell, District Manager Criminal Investigations, says it is a significant result for police and Customs staff, and will "go a long way to help keep our communities safe".

"These drugs, should they have made it to the streets, would have caused significant harm to people and communities, not just in Canterbury, but across the country," Parnell said.

"Methamphetamine is a destructive drug that wrecks lives, breaks down whanau and negatively impacts on our community.

"It takes enforcement and a whole-of-Government approach, along with education to reduce demand and victimisation caused by this drug."

Customs Manager Central and Southern Ports Joe Cannon says the operation shows the close-knit relationship between Customs and Police, as both agencies work together to disrupt meth supply in the communities and regions.

"This seizure was the result of risk-profiling and targeting work that Customs carries out for all goods, people and craft coming into New Zealand - whatever the region or method of import," Cannon said.

"We maintain a national perspective to protect our border, and will do everything possible to keep this hideous drug away from our communities."

If you have concerns about any person who is using or abusing drugs, please contact the Drug Alcohol Helpline on 0800 787 797 or click here for information and support.