The man, aged 30 to 35, had 13 stab wounds in his chest and abdomen, paramedics discovered once the body was lifted onto the pier at Rassada in Phuket City.
He had also been hit with something solid, Phuket City police believe. They were called to the scene about 7.50am today.
The man, yet to be identified, could be Thai or Burmese. Police think a frenzied attack may have followed a dispute.
He has a blue eagle tattoo on his chest. The body was taken to Vachira Phuket Hospital in Phuket City.