Relatives of a British couple whose yacht is thought to have been hijacked by pirates off the east coast of Africa said they feared the "worst might have happened".

A rescue mission was under way to locate Paul and Rachel Chandler, from Tunbridge Wells, Kent, after they went missing while sailing from the Seychelles towards Tanzania.

A news agency said it had been contacted by a pirate to say the couple were "in our hands now".

The man, who gave his name as Hassan, said the captives were in good health and ransom demands would follow. The Foreign Office said it was "urgently investigating" the claims.

Leah Mickleborough, the couple's niece, said the family were alerted to an alarm signal made from the couple's yacht - the Lynn Rival - on Friday but initially thought the situation was not serious.

"We were just waiting for them to come into docks because it tended to be the case that, out in the middle of the Indian Ocean, it was quite difficult to get hold of them and it was expected that they would dock at a little island," she told Russell Fuller on BBC Radio 5 Live.