The six passengers, all police officer, lost their lives after the small aircraft plunged into the Gulf of Thailand off the coast of Cha-am in the southwest of the country at around 8.25am local time (2.25am in UK).
Police confirmed the crash happened during its force's test flight mission to prepare for a parachute jump training exercise.
The Royal Thai Police would like to express their deepest condolences and sympathy," the force said in its latest update. It added the six passengers include the pilot, also a police employee.
Photographs show the wreckage in the water and emergency services gathered, following their desperate scramble to locate the plane and help those inside.
They arrived to find four people had passed away instantly and, despite the best efforts of medics, the other two officers have also been declared dead. One man, thought to have been the pilot, was rushed to hospital, where he died.
The identities of those killed in the Thailand disaster have not yet been disclosed. An investigation into the cause has been opened, though Police General Kittirat Phanphet, the national chief, has travelled urgently to the scene to oversee operations and monitor the situation. The boss said: "The families of the victims will be closely supported and funeral arrangements will be made for them. I have ordered a detailed investigation into the cause of the crash."
