Military men in colourful hats carried a gilded palanquin through Bangkok's old quarter Sunday in a dress rehearsal for the royal procession of Thai King Maha Vajiralongkorn's coronation—a once-in-a-lifetime spectacle marked by pomp and ancient tradition.

The royal coronation of the 66-year-old monarch will run from May 4-6 and is considered the most important event of the year in Thailand.

It is the first in 69 years since his revered late father Bhumibol Adulyadej—who passed away two years ago—formally took the throne in 1950.

The ceremony's second day is the royal procession, during which King Vajiralongkorn will be elevated on a palanquin carried by soldiers.

It will leave from the Grand Palace and circle around the historic old quarter, giving the people a chance to pay homage to their new monarch.

Sunday's rehearsal proved to be a draw for dozens of bystanders curious about the elaborate ritual.

A colourful array of traditional garb was on display—from pointed red hats to puffy golden-yellow helmets—as soldiers carrying embroidered tiered umbrellas marched in lock-step to beating drums.

Junta leader Prayut Chan-O-Cha, donned in full military regalia, also took part in the procession.

"I've come to watch the rehearsal today because it is an important ceremony that I've never seen before in my life," said Somchai Weerathamsathit, who works in an automobile factory.

The 51-year-old had been waiting under the scorching sun for two hours for the procession, along with thousands of security and state officers dressed in yellow polo shirts.

In the weeks leading up to the coronation, state officials have started to wear yellow, considered to be the king's colour. TV anchors have also taken to wearing the colour during nightly newscasts.

The monarchy—one of the richest in the world—is considered sacred in Thai society.

It is protected by a draconian royal defamation law, rendering open discussion of the royal family to be all but impossible.

See also: Memories of HM King Bhumibol Adulyadej's Teachings