Packets of fentanyl mostly in powder form and methamphetamine, which US Customs and Border Protection say they seized from a truck crossing into Arizona from Mexico, is on display during a news conference at the Port of Nogales, Arizona, US on January 31 2019. Photo: VCG

Smugglers disguised $3 million of methamphetamine as onions and tried to get the drugs into the US in a shipment of vegetables, customs officers said.

A trailer loaded with the pungent bulbs was stopped as it crossed from Mexico when a drug dog was alerted by a strange smell.

Among the tens of thousands of regular onions, border agents found almost 1,200 packages of methamphetamine, shaped into small globes with a white covering and apparently intended to look like the vegetable.

"This was not only a clever attempt to smuggle narcotics, one I haven't seen before, but also time consuming to wrap narcotics into these small packages, designed to look like onions," said Sidney Aki of US Customs and Border Protection in San Diego.

"While we have certainly seen narcotics in produce before, it's unusual for us to see this level of detail in the concealment," he added.