Pol Lt Col Somkiat Sarasit of the Chalong was informed of the assault at about 3:30pm.
Officers and rescue workers arrived at the scene, in Soi Khoktanod-Chaloem Phrakiat, opposite Wat Ladthi Wanaram (Wat Tai), in Chalong, to find Kiadtisak Mannun, 21, from Krabi, on the ground with a large slash wound on his right arm.
Rescue workers administered immediate first aid before rushing Mr Kiattisak to Chalong Hospital.
Officers are now checking CCTV in the area for clues to track down the perpetrator, Chalong Police reported.