A drug considered a potential chemical weapon and terrorist threat has been detected in Queensland, sparking an urgent warning from authorities.

The synthetic drug carfentanyl - about 10,000 times as potent as morphine - has been intercepted by border force officers at a Brisbane mail centre.

The elephant tranquilliser is typically sourced from China, which announced a ban on it this week, and is so deadly to humans it can kill on contact.

It's only the second time carfentanyl has been detected in Australia, with a quantity uncovered at a Sydney mail centre late last year.

Authorities won't reveal how much of the drug was seized but are concerned about even the smallest amount making its way onto the streets given a dose as tiny as 0.002mg can kill.

Carfentanyl, based on fentanyl, has been linked to thousands of deaths across the world in recent years.