At the scene rescue workers found the body of Chupchai Jankaew, 43, from Thung Song in Nakorn Sri Thammarat, lying on the right-hand lane on the road exiting the underpass.
His motorbike was lying on the road some 15 metres further ahead.
Mr Jankaew’s relatives have been notified of his death, police confirmed.
After police had inspected the scene, rescue workers transported his body to Vachira Phuket Hospital in Phuket Town.
At this stage police have yet to confirmed how the accident transpired.
Lt Wipawan Wattanangerntanong of the Phuket City Police confirmed to The Phuket News that an investigation had been launched to determine was caused the death.