The sudden plunge in demand for scrap metal is causing a headache for port authorities around the world with tonnes of steel left on the docks as buyers default on purchasing.

The Scrap Metal Recyclers Association says that six weeks ago, many recyclers were paying $360 a tonne for heavy steel scrap.

A sudden plunge in world demand has seen that fall to a mere $60.

Association spokesperson Karina Munro said that suddenly wharves around the world have tonnes of scrap metal sitting on them as buyers default, and as demand drops.