An off-duty policeman allegedly shot dead one taxi motorcyclist and wounded two others during an argument over a fare, in Bangkok's Din Daeng district early Sunday morning.

The shooting at the entrance to soi Pracha Songkroh 38 was reported to Huai Khwang police about 2.50am.

At the scene, officers found taxi motorcyclist Purit Mangthisan, 37, lying dead with several bullet wounds in his back and exit wounds in his chest. 

Two other riders were wounded. Kiatisak Srirat, 46, was shot once in his thigh and Charin Khunarak, 48, had bullet wounds in his thigh and hand. They were taken to separate hospitals.

Eyewitnesses said the shooter approached a group of taxi motorcyclists who were relaxing. The two sides began to argue and the shooter drew out a gun and fired multiple shots at the motorcyclists.

A man later surrendered at Makkasan police station. He was identified as Pol L/C Namthap Pakwatana, 33, a border patrol policeman. 

Pol L/C Namthap allegedly told police the shooting arose from a dispute over a fare. He alleged the taxi motorcyclists assaulted him first and he fired his gun in self defence.

Surveillance camera footage confirmed that two taxi motorcyclists had begun assaulting him before the shots were fired.

A relative said Pol L/C Namthap had a mental condition and took prescribed medicine.

The police investigation was continuing.