This is the heartwarming moment a lost dog was rescued after being found swimming in the ocean.

A ferry was taking workers to a hotel when they passed by the black dog drifting in the waters yesterday morning (September 24).

The boat had set off from Rayong in eastern Thailand to Koh Samet island around five miles away.

Passengers noticed the hapless dog struggling in the middle of the deep sea around two miles from land and immediately set about trying to help.

A passenger told the ferry captain about the drowning dog so he stopped the boat for a moment before a brave hotel security guard jumped in the water to save the dog.

He was only wearing socks and underpants as he pulled the struggling dog towards the boat.

The ship's crews then lifted the dog on board from the small window followed by the man who went up using a rope.

A hotel worker who witnessed the rescue, Khai, believes the dog had leapt from a ferry before trying to swim back to the island.

She said: ''The dog was so far from the land it must have fallen from a boat. I think it could have boarded one by mistake then jumped overboard.

"The dog was lucky to have survived the deep water. We were all happy that our teammate saved its life. We are so proud of him."

The dog was later taken back to the port and was reunited with its owner, who had been looking for the dog. He believes it had mistakenly wandered aboard the ferry then jumped off after realising it was going away from home.