The incident occurred on Phisit Korani Rd at about 7:55pm.
Officers arrived to find bloodstains on the stairs of a fitness building under construction. The victim had already been taken to Patong Hospital by a good Samaritan.
Two Myanmar nationals who witnessed events told police that around 7pm, two Thai men with long hair and beards approached them, along with another Thai man wearing a vest, asking to borrow flashlights. The men said they were looking for a thief who had stolen their motorcycle and fled into the unlit building.
The witnesses said that after lending them the flashlights, the men later asked them to call an ambulance. Inside the building, the witnesses discovered a man lying on the stairs, bleeding from multiple stab wounds. They carried him outside and handed over the knife believed to have been used in the attack.
Rescue workers arrived at about 7:30pm and transported the injured man to hospital. He was later identified as Wiset Kaenwong, 49, of Patong.
Mr Wiset suffered knife wounds to his left shoulder, chest, both legs and head. Police collected a bloodstained knife and a bamboo stick from the scene as evidence.
Officers confirmed that they are working to track down the two Thai suspects and bring them to justice.