Police were investigating today (Wed) after a tourist was found floating in the sea with an 8kg rock tied around his neck.

The western man, whose nationality is not yet known, was see off the coast of Pattaya, eastern Thailand, yesterday (Feb 11) afternoon at 1:30pm local time.

Shocked locals called police in the notorious Sin City resort - a well-known destination for criminals - who are considering whether the man was murdered by being thrown off a boat with the stone attached, leaving him unable to swim to safety.

They said the heavily-set man was in his 50s and had been dead for between one and two days.

Officers are also considering whether he had the rock tied to his neck before being pushed from a boat, causing him to drown.

Captain Nakhonrat Nontseelard from Pattaya Police said: ''We don't know how the man died but an autopsy should give us a better idea.

''If he was pushed into the water he would not be able to swim. That would be murder.''

The victim was found in the sea around 400 meters off the coast of Koh Larn, a small island popular with tourists.

Pictures from the scene show he was wearing blue denim shorts, grey flip-flops and a grey to-shirt.

A black leather ruck sack with a phone charging cable, neck pillow, belt and several personal items, also found with the man.

Police said it was possible that he tied the rock around his own neck before jumping into the sea from a pier. The decomposing corpse would then have risen to the surface.

Police Captain Nontseelard added: ''The man could also have been dead before he was thrown into the sea and the rock used to try and conceal the body. Every option will be considered.

''If anybody knows of a tourist who has gone missing they should contact police with any information they have.''

Thanonchai Rienpreecha, one of the paramedics from the Sawang Boriboon Foundation that attended the scene, said: ''The foreign man was lying face down with a rope to tied his neck and attached to a large stone.

''There is no clear cause of death but a forensic examination will show if he died from drowning or if he was killed first then thrown into the sea.''