Access World in a statement urged holders to seek authentication of the receipts for commodities such as copper and aluminium, which are typically used as collateral for bank finance.

Metals markets were rocked more than two years ago by a $3 billion (2.4 billion pounds) fraud at Qingdao port in China, when a firm allegedly duplicated warehouse certificates to pledge metal as collateral for multiple bank loans.

"Access World has become aware that there are forged warehouse receipts in our name circulating in the market," the company said in a statement issued late on Friday.

"We encourage holders of any Access World warehouse receipts to seek authentication from the relevant issuing office for any warehouse receipts not issued to them directly by Access World."

A spokesman for Glencore declined to comment

(Reporting by Melanie Burton; Editing by Richard Pullin)