Police have launched a murder investigation after a missing family of five including a baby was found shot and stabbed to death in northern Thailand.

The parents and their three children had been missing since Sunday but their decomposing bodies were discovered in Tak province close to the border with Myanmar on Wednesday morning February 8.

Police said the grim discovery included the father Chaow Manpattanakan, 46, his wife Jia Saengsawang, 34, their two sons Phiphiboon, 10, Ekkaphon, 7, and three-month-old baby daughter Waranya.

Officers sealed off the area, which was in a field by the Nakheeree stream around six miles from the village where the young family lived together. They were all of Hmong hill tribe origin.

Police Colonel Wasan Sirikankomol, a superintendent of Wang Chao distirct police station, said officers are searhcing for suspects 'who had a grudge against the family'.

The policeman said: 'We arrived at the scene at 10 AM after receiving a report from the village chief.

'The initial position was that this is a murder case. We are searching for suspects. The bodies had gunshot wounds and stab wounds. We collected one 9mm bullet shell and a black plastic bag from the scene.

'Police forensic officers are searching the area for other pieces of evidence. There are not any CCTV cameras.'

Officers said the cause of death has not been confirmed as it was difficult to check the bodies of the suspected victims. However, the police chief said that investigators had found a slash mark wound on Chaow's throat.

Investigators were visiting the scene again on February 9 to inspect the area while the bodies were undergoing post-mortem examinations.

Police Colonel Wasan added: 'The motive for the murders is currently under investigation but we believe that the murderer held a deep grudge against the family.

'The victim's relatives and the suspect are being questioned.'

Police said that the family had been uncontactable since February 5 when they failed to return home after work.

The husband's father said that he has not seen his son since the New Year holiday at the end of December and early January.

He said that residents in the village started to notice that they were missing after their children were absent from school. He said that his son had worked in this area for around 10 years.

The father said he was unaware of any disputes his son had as they were not living together.