Zanzibar, Tanzania - An active search for four missing Danish divers and their Canadian instructor - who disappeared in Indian Ocean waters off Zanzibar nine days ago - has been called off, officials said on Monday.

With virtually no hope of finding the divers alive, the company that organised the ill-fated July 16 trip said only passive searches for the bodies of the missing were still under way on and around Pemba and Misali islands and parts of the nearby mainland Tanzanian and Kenyan coasts.

"We have called off our active search," said Farhat Jah, the owner of Pemba-based Swahili Divers. "I myself have lost all hope of finding them alive."

Police on Tanzania's semi-autonomous archipelago of Zanzibar and Pemba said they were still looking although chances of recovering the divers were slim.

"We have not discovered anything so far," Pemba regional police commander Ameir Juma Ameir told reporters.

The five missing divers, who were among a group of 14 on a Swahili Divers outing, were reported lost when they did not return to the dive boat after heading off in another direction from the other nine.

Since then, Zanzibar police and hundreds of volunteers have led a fruitless air and sea rescue operation that has turned up little evidence as to their whereabouts or what might have happened to them.

Jah told reporters on Monday that the disappearances were a "complete mystery", noting that the four Danes were all certified divers and the Canadian instructor an experienced divemaster with more than 8000 dives under his belt.

"All the evidence we have gained points towards an underwater catastrophe of some sort, something like a down current, something so strong that took our most experienced divemaster," he said.

Police have identified the missing Danes as Dannie Schov and her two sons, Gabriel and Simon Lowestan, and Lisse Lotte.

The missing Canadian dive instructor has been identified as Neil Clark. - Sapa-AFP

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