Thaksin Shinawatra was transferred from Bangkok Remand Prison to the Police General Hospital at 12.20am Wednesday, suffering from chest pain, hypertension and low blood oxygen, the Department of Corrections said.

The department said a warder at the prison reported that Thaksin could not sleep, had chest pain, hypertension and low blood oxygen.

Thaksin was admitted to the prison on Tuesday afternoon after his return to Thailand on Tuesday morning, following a court appearance.

A doctor at the Corrections Hospital reviewed Thaksin's symptoms and considered his medical treatment records from overseas hospitals, which diagnosed him with several underlying illnesses.

As the Corrections Hospital lacked some medical equipment, the doctor decided to transfer Thaksin to Police General Hospital, which was better equipped, for his safety.

Thaksin was admitted to Police General Hospital for treatment and prison staff were deployed there in line with the regulations of the Department of Corrections, the department said.

The Police General Hospital said in a statement on Wednesday that a Corrections doctor checked Thaksin's symptoms and found his illnesses required urgent treatment.