Well-wishers pray for the healthy recovery of King Bhumibol Adulyadej at a hospital in Bangkok. The world's longest reigning monarch is in unstable condition after undergoing blood dialysis. (Diego Azubel/European Pressphoto Agency)

The children of King Bhumibol Adulyadej, the Thai monarch revered as a figure of unity and stability in a country prone to political turbulence, gathered at his bedside on Wednesday as the palace issued a new report on his deteriorating health.

Crown Prince Vajira­longkorn flew in from Germany, where he has a residence, and Gen. Prayuth Chan-ocha, the prime minister and junta leader, cut short a trip outside the capital amid growing anxiety about the condition of the world’s longest-reigning monarch.

The 88-year-old king is on a ventilator battling fresh infections after receiving blood-cleansing dialysis treatment over the weekend, according to the latest palace update. His health has “overall not yet stabilized,” the statement said.

The Bangkok stock exchange plunged sharply, and many Thais donned pink clothing — regarded as a lucky color by royal astrologers — while hundreds of well-wishers converged on the riverside hospital that has been his main home in recent years.

The military government urged Thais not to listen to “uncorroborated information” on social media but rather to await “official announcements for an update on the situations,” without giving further details.

Thailand's 88-year-old king is said to be in an unstable condition in hospital after undergoing dialysis. (Reuters)

The junta spokesman played down Prayuth’s abrupt return to Bangkok, saying that he met the crown prince “for a routine presentation” on government matters, just hours after the heir presumptive arrived in the country.

On Sunday, doctors for the king, who has not been seen in public since January, reported that they had sought formal permission for him to cease official duties.

In a country where harsh lese-majeste laws are in place, public discussions about the king’s health and royal succession issues are strictly curtailed.

But this week’s two bulletins triggered sharp slides in the stock market and the value of the Thai baht in a country where the military took power in 2014 after years of political turmoil.

The king has reigned for 70 years after ascending the throne following the death, by a single gunshot, of his older brother in mysterious circumstances.

During a series of coups, he was seen as a stabilizing factor.

The king’s ailments chronicled in previous updates included a series of infections, breathing difficulties, renal failure and “water on the brain.” In the latest statement, the palace said that doctors used drugs to control his blood pressure and performed renal replacement therapy.

Outside Siriraj hospital, Thais lined up to buy pink clothing at nearby street stands, and many held up his portrait.

Wanna Sirikhet, 69, told the Bangkok Post that she traveled nearly 700 miles from her southern home town to offer her best wishes. “I came here to pray for the king, and I believe that millions of Thais nationwide are now praying for his quick recovery as well,” she said.