Greek authorities are still desperately searching for a missing British woman who vanished from her sunbed on a Greek beach while her husband was asleep.

Michele Ann Joy Bourda, 59, had been swimming at Ofrynio beach in the city of Kavala at around noon on Friday before disappearing.

The police have been conducting a search on land for the tourist, while Greece's Hellenic Coast Guard have been searching in the sea, but the central port authority in Kavala told the Daily Mail that rescuers might call off the operation by the end of the day on Monday.

A Silver Alert was issued after the police failed to immediately locate the tourist and authorities have warned that she may be in danger.

A map shows how the 10.5 mile long Greek beach where Bourda vanished after lounging on a sunbed is surrounded by expansive fields, residential houses and a huge fishing pond.