This is the heartwarming moment a fisherman released an enormous green sea turtle he accidentally caught in Thailand.

Anad Masosot, 35, was fishing for mackerel in Ao Nang sea off the coast of Krabi province when he encountered the reptile on December 9.

The experienced angler boarded his boat, patiently waiting to hook a mackerel on his fishing rod.

The boat has reached three nautical miles away from the shore after 20 minutes when he felt something heavy tugging it.

He excitedly pulled the rod hoping that he caught a big fish until a strange flipper became visible from the water.

Anad was surprised that he had caught a big sea turtle that weighed almost 17 kilograms.

The man reached for the creature's flipper and carried it into the boat to unhook it before tossing the turtle safely back into the sea.

He said the turtle may have been attracted to his fish bait but it was trapped in the net instead.

Anad said: "I thought I caught a huge fish because it was heavy. I returned it to the water afterwards and swam away."

The green sea turtle was uninjured and the fisherman continued catching mackerel in the area.

Green sea turtles are one of the world's largest species of turtle that can weigh up to 130kilograms and reach up to more than one metre long.