Bhumibol Adulyadej
Well-wishers hold a picture of Thailand's King Bhumibol Adulyadej at the Siriraj hospital where he is residing, in Bangkok, Thailand, June 9, 2016 Reuters

Thailand's ailing monarch King Bhumibol Adulyadej is "not stable" and is on a ventilator, palace officials have said.

Bhumibol is the world's longest-serving monarch and is highly popular among his people. However, he has not made any public appearance for nearly a year after being hospitalised in Bangkok after being diagnosed with a series of ailments.

For the last two years, the 88-year-old king is being treated for infections, breathing difficulties, heart problems, renal failure and hydrocephalus, a condition in which cerebrospinal fluid accumulates in the brain.

However, the palace has always been tight-lipped about the monarch's health conditions. It is only recently that the officials are issuing more regular updates.

According to Agence France-Presse, The Royal Household Bureau said that a ventilator was deployed after the monarch suffered a sharp drop in blood pressure. The incident happened following the procedures to prepare him for dialysis and to change the tube that helps to drain out fluid from his spine.

"The medical team is watching his symptoms and giving treatments carefully because the overall symptoms of his sickness are still not stable," the statement said as reported by the news agency.

According to Reuters, Princess Chulabhorn, the king's youngest daughter, said in a television statement in 2011 that the king had suffered a health scare and fell unconscious after internal bleeding likely induced by stress.

King Bhumibol Adulyadej has ruled for seven decades and the Thais are concerned about losing their monarch. AFP reported analysts argue that the anxiety over the end of Bhumibol's reign has been aggravated by the political turmoil in Thailand in the past decade.

The King and his family have been protected by one of the world's harshest royal defamation laws. Anyone who insults or threatens the king, queen, heir to the throne or regent will be criminalised and prosecuted.