A portrait of Thailand's late King Bhumibol Adulyadej is seen among garlands at the Siriraj hospital in Bangkok, Thailand, October 14, 2016. [Photo/Agencies]

Queen Sirikit, 84, has also been in poor health over recent years.

The government has set up a telephone hotline to help people cope with grief, a spokesman said.

Prayuth warned against anyone taking advantage of the situation to cause trouble. Politicians from all sides will be in mourning.

Thai stocks and the baht currency are likely to be volatile in the short term and consumers could cut spending, but assuming a smooth transition, major economic disruption was not expected, the Eurasia Group of risk analysts said in a report before the king's death.