His body was due to leave Bangkok's Siriraj Hospital for the Grand Palace, where his funeral rites will be carried out.
Somdej Phrawannarat, a much-revered monk, will lead the procession, the palace said. Phrawannarat is a leader at a Buddhist temple that is important to the King's Chakri Dynasty. He will be followed by the Crown Prince Maha Vajiralongkorn.
The King's body and his family will then travel by motorcade to the Grand Palace, where mourners have already begun to claim spaces to watch the historic event. Many have been camped out as early as midnight.
"I couldn't sleep and I didn't want to sit around at home, I had to do something as I was feeling so sad," says Patarapong Chankaw, 28. "So I came to the grand palace to be with other mourners."
He's been at the Grand Palace since 5 a.m. local time and plans to stay until the procession is over.
Once the body arrives at the palace, it will undergo a funeral bathing ceremony -- a traditional rite in Buddhist culture.
Thais have also lined up for the opportunity to pour water on a portrait of the King inside the palace grounds -- a way for the masses to simulate the symbolic royal bathing of the King's body.