A Moroccan tanker carrying 5,000 tonnes of fuel that ran aground during a storm last month will have been pumped dry by Monday without any lasting environmental damage, the environment minister said.

The Moroccan-flagged "Silver" hit rocks near the Atlantic port of Tan Tan during a storm on December 23, and there were fears of an ecological disaster.

After several unsuccessful attempts to refloat the vessel, authorities brought in scores of fuel trucks on Tuesday to pump out the fuel.

Since then, "two thirds of the cargo has been offloaded," Environment Minister Abdelkader Amara said Saturday.

"Expectations are that the operation will be completed over the two days (ending Monday), and the cargo will have been totally removed," he added.

After that, engineers will again try to refloat the vessel.

The ship was travelling from the Canary Islands when it ran aground, with heavy waves dragging it towards a rocky area, sparking fears of an oil slick on the coast.

Amara said while small leaks into the sea have been reported, "international experts I have met have assured me that there are no (lasting) pockets of pollution."

The fuel was being transported to a power station in Tan Tan, which lies close to the Western Sahara, about 300 kilometres (190 miles) south of the Moroccan resort town of Agadir.