HONG KONG (AFP) - Hong Kong conservationists have expressed outrage after images of a factory rooftop covered in thousands of freshly sliced shark fins emerged, as they called for curbs on the "barbaric" trade.

The southern Chinese city is one of the world's biggest markets for shark fins, which are used to make soup that is an expensive staple at Chinese banquets and viewed by many Asians as a rare delicacy.

Activist Gary Stokes, who has visited the site, estimated there are 15,000 to 20,000 fins being laid to dry on the rooftop on Hong Kong island ahead of an anticipated surge in demand over Chinese New Year in February this year.

"This is shocking," the Hong Kong coordinator for conservation group Sea Shepherd told AFP, saying it was the first time he had spotted such a massive hoarding of shark fins in one place in the Asian financial hub.

"This is the most graphic, brutal and barbaric part of the industry - the element of chopping a shark's fin off and throwing it back into the water is horrific and inhumane," he added.