A shipment from South Africa of enough deadly drugs to wipe out over 220,000 people has been discovered by US law enforcement officials.

The lethal drug fentanyl is an addictive synthetic opioid that's often added to heroin. The package had a street value of over R1.4 million.

A statement from the US Customs and Border Protection agency said the drugs were labelled as water purification chemicals. They were sent to an address in a small town in the state of Colorado.

The shipment, which was seized on 21 September, also contained a small bag of cocaine valued at about R60,000. It had been marked as a magnesium mix. A small bag with more fentanyl had been labelled as "bicarbonate minerals", Business Insider reports.

The agency did not disclose exactly where in South Africa the shipment was sent from. But it was seized in the port of Louisville, Kentucky.

Louisville's port director Thomas Mahn said: "Our officers are committed to keep our country and communities safe from illegal and dangerous drugs."

"This seizure is one example of the quality enforcement work they do on a daily basis," he said.