BANGKOK - THAI authorities charged a third person on Tuesday with spreading false rumours about the health of the country's revered king, after concerns about his condition sent markets plunging, police said.

Somjet Sitthiworakul was arrested at his home near the resort of Pattaya for allegedly damaging national security by posting false information on the Internet, a day after police said they had charged two other people.

King Bhumibol Adulyadej, who is regarded as a demi-god by many Thais and as a stabilising force in a politically turbulent nation, has been in hospital since mid-September with a lung infection and fever.

'A third suspect has been arrested by the investigation team on Tuesday and charged with violating the computer act,' Police Lieutenant General Thangai Prasjaksattru, chief of the central investigation bureau, told AFP.

He had no further details about Somjet's age or occupation.

The Thai bourse plunged 8.22 per cent at one point on Oct 15 over rumours about the health of the 81-year-old king, the world's longest reigning monarch, prompting the government to launch an investigation. -- AFP