THIS is the incredible moment missing Brit castaway Mary Gavin waved desperately at a passing ship after being stranded in the sea for five days.

Footage shows Ms Gavin in a life jacket shouting for help after she vanished on a boat she had rented on a Spanish paradise island.

She was rescued alive on Saturday after passengers on a passing ferry headed to Valencia spotted her and raised the alarm.

The 39-year-old Brit was then rushed to a hospital to receive medical treatment.

Emergency rescuers revealed Ms Gavin rented a Quicksilver 475 Axess boat in Formentera before she lost her way in the middle of the sea last week.

Alejandro Rosera, one of the passengers on the ferry that rescued her, said that she was dehydrated and had severe sunburn.

Ms Rosera added: “When we were about to pass by Formentera, we were told there was an emergency and we had to turn back.

“Later on, we saw a woman on board a small boat. “She had a life jacket on and another in her hand, making gestures.

“She was dehydrated and sunburnt and had mouth sores.

“Once we got to Valencia, a large number of police and health professionals were waiting for her and assisted her immediately.”

Police and coastguards started hunting for Ms Gavin last Wednesday – some 36 hours after she vanished after renting the boat from Formentera.

Expert divers were tasked by the Spanish coastguards to scour the depths of the ocean to search for the missing Brit

The Spanish Civil Guard also mobilised helicopters and boats in a bid to find clues about her.

Cops revealed that friends of the Brit woman first raised the alarm after she failed to return from her boating trip.

“From the time she was reported missing on Wednesday evening, a search operation was launched, and it continued throughout the day,” they added.

After rescuing her, a Civil Guard spokesman said: “The British woman who vanished after renting a boat in Formentera on Tuesday morning has been found alive.

A police source said last week the missing woman had been living on one of the Balearic islands for around two months.

Although it was not immediately clear whether the island is Ibiza or Formentera.

No more details have been given out by local authorities about what they think went wrong and why the woman ended up adrift in the middle of the sea.

Last year, four people including two Brits were dramatically rescued from a stricken boat after getting lost at sea for four days.

The dehydrated men were found by Spanish authorities some 60 miles off the coast of Tenerife.

They made a Mayday call to alert local ships after being stranded in the sea for days.

A Panamanian-flagged ship along with a Spanish Civil Guard vessel is said to have responded by heading to the area they were in.