Thailand's crown prince will lead a mass cycling event Friday in tribute to his father King Bhumibol Adulyadej, a rare public appearance for the prince amid anxiety over his ailing dad's health.
Prince Maha Vajiralongkorn, 63, will ride with tens of thousands of yellow-clad cyclists through the streets of Bangkok for the "Bike for Dad" event, a nod to the king's official colour. A similar mass cycle in August celebrated the role of his elderly mother Queen Sirikit.
The mass cycling events have been billed as a chance to promote unity among Thais 18 months after a coup swept away the civilian government -- the latest episode in a seemingly endless succession of elections and coups.
For weeks, television presenters have been wearing yellow shirts in the run-up to the king's birthday last Saturday, which was a subdued affair with no statement issued or public appearance made.
The king is revered among many Thais but has been in hospital for much of the last two years and is rarely seen in public.
Police have closed normally busy streets and cyclists were gathering at the Royal Plaza in central Bangkok early Friday, from where they will set off to ride a 29-kilometre (18-mile) route through the capital.
According to official figures, more than half a million people nationwide are expected to take part in Friday's cycling event, topping the 136,411 people who participated in the "Bike for Mom" event in August.
The two tightly-choreographed mass cycling events have thrust the crown prince centre stage at a time of heightened concern over the health of his revered father and over the political and economic fortunes of the country.
In recent years, Prince Vajiralongkorn has spent much of his time away from the public eye.
But he has stepped in at some official ceremonies as his father's health declines.
For much of the last decade Thailand has been rocked by political instability partially fuelled by jostling among the country's elites for influence as the king's reign enters its twilight years.
Bhumibol and his family are protected by one of the world's harshest lese majeste laws, making criticism of the monarchy, or public debate about its role in society all but impossible.
The interplay between the monarchy, politics and the people is delicate and heavily shrouded by the law.
Convictions under the controversial legislation have skyrocketed since the country's royalist military seized power last year, toppling a democratically elected government.
