An investigation has been launched into why ambulance staff dumped an ill, Pattaya state-hospital patient in an open field.

Deputy Public Heath Minister Wicharn Meen-chainant is demanding an immediate investigation.

People report they saw an ambulance leave the man in an open field late Tuesday night. Pairat Boonkrong was discovered shivering and incontinent under a tree. He had wrapped himself in a blanket and huddled under a tree for shelter. The blanket is the property of the Bang Lamung Hospital. Prescription medicines were discovered nearby.

Pattaya City Councillor Sanit Boonmachai called the hospital director, demanding the ill man be returned to care.

Prasit strongly denies suggestions the hospital deliberately abandoned the patient. "It's a misunderstanding," Prasit says.

Pairat is suffering from pneumonia and was admitted to the hospital on Monday. It says he was discharged the next day. But, because no one came to collect Pairat, an ambulance took him home.

The ambulance driver claims Pairat asked to be dropped off after he saw a "friend passing by".