Pol Lt Col Charuwit Khuncharoen of Chalong Police Station was informed of the accident by the 191 emergency centre at 9:10pm.
At the scene, officers found a Royal Enfield Interceptor 650 motorcycle, registered in Phuket, on its side in the tunnel.
The rider, identified as Anan Manma, 39, had sustained fatal injuries and was pronounced dead at the scene. His passenger, Busaya Manma, 34, suffered injuries and was rushed to Chalong Hospital.
Chalong Police Chief Pol Col Rungrit Rattanaphakdee was notified of the incident and coordinated with patrol officers and rescue workers to manage the scene and restore traffic flow.
Mr Anan’s body was later transferred to Vachira Phuket Hospital for further examination.
Police said the exact cause of the accident remains under investigation.