Phuket City Police said the arrest was made during a checkpoint operation conducted between 1am and 2am on Ruam Pattana Rd in Ratsada.
The operation was carried out under the direction of Phuket City Police Superintendent Pol Col Chatree Chukaew and led by patrol officers including Pol Lt Col Sarun Chaiwut, Pol Lt Col Piya Yongpraderm and Pol Lt Theerasak Thongnoon, together with motorcycle patrol officers.
Police said officers searched 30 people, 10 cars and 20 motorcycles during the operation.
One suspect, identified only as ‘Mr Nutt’, 18, was found in possession of a firearm and 11 rounds of .380 ammunition.
He was taken to Phuket City Police Station for questioning and formal arrest procedures.
Police charged him with possession of a firearm and ammunition without a permit, possession of an unregistered firearm and possession of a modified blank gun, along with illegal possession of 11 rounds of .380 ammunition.
The arrest comes just days after Wichit Police announced the arrest of several teenagers linked to shootings in Wichit and Kathu, including an attempted murder case at Laem Dinso viewpoint and another attack in which gunfire damaged a vehicle in Kathu.
Police in that case seized homemade firearms, ammunition and spent shell casings, while multiple juvenile suspects were charged with attempted murder and illegal firearms offences.