BANGKOK (AP) -- Thailand's crown prince led tens of thousands of cyclists on a 29-kilometer (18-mile) ride through Bangkok on Friday to honor his father, King Bhumibol Adulyadej, whose declining health is a matter of national concern.
The event called "Bike for Dad" comes a week after Bhumibol's 88th birthday, which is a national holiday celebrated each year as Father's Day in Thailand. The once-vigorous monarch, who is widely revered in Thailand, is frail and ailing and hasn't been seen in public since September.
Some 100,000 people signed up for the ride, all wearing shirts in bright yellow, the king's color. The typically traffic-clogged Thai capital closed off dozens of streets, including some of the city's busiest roads, for the high-profile event that was carried live on all public television stations.
It was the latest mass cycling event organized to promote Crown Prince Vajiralongkorn at a time of concern about the royal succession in Thailand. He led a similar event in August called "Bike for Mom" to celebrate his mother, Queen Sirikit's 83rd birthday.
Until this year, it was rare to see the 63-year-old crown prince outside of formal ceremonies or mingling with the public. The king's only son and heir apparent does not command the same affection as his father, though open discussion of the monarchy is constrained by a strict lese majeste law that makes criticism of the royal family punishable by up to 15 years in prison.
Bhumibol is a constitutional monarch with no formal political role but he has been regarded as a stabilizing figure for Thailand and earned national respect for dedicating himself to public service in his younger years. Bhumibol looked frail on his last public appearance on Sept. 1, when he was taken on a brief tour of the Bangkok hospital where he has spent most of the last six years.