Thais on Tuesday wore pink for 88-year-old King Bhumibol Adulyadej, a colour they believe will help improve the monarch's health, two days after the palace said he was in an unstable condition.
King Bhumibol, the world's longest reigning monarch, is widely revered in Thailand. During his seven decades on the throne the king, who is also seen as a unifying force for the country, has intervened when events threatened to plunge Thailand into crisis.
The palace said on Sunday the king's health was "not stable" following haemodialysis treatment in hospital, a process to purify the blood. It said a ventilator was deployed after the monarch's blood pressure dropped.
It is unusual for the palace to state that the king's health is not stable. Statements on the king's are usually issued after the monarch's condition shows improvement.
Many Thais are highly superstitious and some believe brightly coloured clothes can attract good luck.
Messages shared on social media since the palace statement have urged Thais to wear pink, a colour which first became important a few years ago when royal astrologers said it was good for the king and would promote wellbeing. Since then, the king has sometimes been seen in public wearing pink.
In Bangkok's Silom district, Chay Chinapairot, 46, a government employee, was among those wearing pink.
"I'm very concerned. I might wear pink every day," he said.
One Facebook page called 'We Love Thai King', which has more than 2.5 million members, used the social media hashtag #wishthathismajestyrecoverssoon in the Thai language.
Prime Minister Prayuth Chan-ocha and members of his cabinet were expected to sign a get-well book for the king at Bangkok's Grand Palace on Tuesday. Wat Pathum Wanaram, a temple in the city's main shopping district, said monks would chant prayers for the king.
Well-wishers on Tuesday flocked to Siriraj Hospital in Bangkok where the king has spent much of the past year.
News about the king's health is closely monitored and the wording of palace statements on the king's health is intensely scrutinized.
Strict laws protecting the royal family suppresses any public discussion of the king's health.