Beheadings and public hangings are part of the work of the cartel CJNG.

Customs investigations manager Bruce Berry told Newshub cartels use intimidation to get what they want.

"These organisations have an international reputation for violence as a method of intimidation, both to get their own means and market share but also in dealing with Government agencies and officials."

Scott Stewart, who works for the geopolitical intelligence firm Stratfor in Austin, Texas, says Mexican crime groups are particularly ruthless.

"[You] quite frequently see abductions where members of rival cartels are kidnapped, dismembered, tortured."

CJNG is just one of the foreign syndicates targeting New Zealand, because Kiwis pay top dollar for drugs.

"In New Zealand a point of meth sells for between $80 and $100. In the US it sells for $5. So these groups look at New Zealand as the golden nugget," National Organised Crime Group national manager Detective Superintendent Greg Williams told Newshub.

CJNG and the Sinaloa Cartel, formerly run by El Chapo, the criminal featured in the Netflix series of the same name, are expanding their influence internationally.

A drug intelligence report on Mexican organised crime says "it's almost certain" such groups "will continue to export illicit drugs, primarily cocaine and methamphetamine, to New Zealand".

"CJNG and the Sinaloa Cartel are currently the only identified cartels engaging in this activity, and are likely to remain the dominant Mexican crime groups in terms of supply to New Zealand," the report says.

Police say it's foreign meth made cheaply and in industrial quantities by global criminal organisations that's addicting and crippling our communities.

"It's having a huge effect in New Zealand right now," Williams says.

Mexican cartels are well-known for corrupting public officials to help them traffic drugs and launder the profits.

The report states: "It's possible that Mexican crime groups will try to corrupt members of border and or law enforcement agencies in New Zealand, to support their activities".

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Mexican cartels are something to be worried about in New Zealand.

"Law enforcement and security agencies in New Zealand need to be very concerned about the potential for bribery," Stewart says.

But Berry says they already do work on organised crime groups at Customs.

"There's always a concern of corruption. We have integrity watchlines, we do regular quality assurance. We talk to our staff around how these organised crime groups work."