Hundreds of thousands of black-clad mourners lined the streets of Bangkok to watch the funeral procession, with buildings on the route draped in yellow marigolds before his cremation.
Mourners slept overnight on thin plastic mats on pavements near the Grand Palace in the Thai capital so they could get a good view of the procession.
"This is the last goodbye. I really love and miss him. It is very difficult to describe," said a tearful Pimsupak Suthin, 42, who travelled to Bangkok from the northern province of Nan.
Officials dressed in blue and orange removed a symbolic golden urn from the Dusit Maha Prasart Throne Hall at the start of the ceremony.
The late king's body, which had been lying in state at the palace since his death, was moved to the cremation area on Wednesday night.
New King Maha Vajiralongkorn, King Bhumibol's only son, arrived at the Grand Palace dressed in a red uniform with his two daughters and young son.
All television stations in Thailand broadcast the ceremony that evoked images of ancient Siam, Thailand's former name.
Flowers, prostration
Officials in charge of the ceremony said around 110,000 members of the public had gathered near the cremation area, with another 200,000 in adjacent areas in the city's historic centre.
A series of processions leading the urn wound through the streets from the Grand Palace in Bangkok's historic quarter to the 50-metre (165-feet) high Royal Crematorium that has been erected in a square nearby.
In other parts of the Thai capital and around the country, 85 smaller replicas of the royal crematorium and more than 870 pavilions were built for mourners to lay sandalwood flowers and pay their final respects to their beloved king.
Many were visibly moved as dozens of men, clad in ancient red garb, pulled the golden chariot carrying the royal urn.
In Nonthaburi province north of Bangkok, a long queue of black-clad mourners waited to place sandalwood flowers to pay their final respects as volunteers handed out food.
Death leaves a vacuum
Piyamat Potsopho, 38, said she had been waiting for the king's funeral procession in Bangkok since Wednesday night.
"I was very fortunate to have been born under the reign of King Rama IX," she said.
Thailand has observed a year of mourning and radio and television stations have played songs dedicated to the monarch almost non-stop. The songs urge Thais to follow in "father's footsteps".
Days of heavy rain failed to deter mourners, many of whom pitched tents in order to gain the best access to the funeral.
King Bhumibol was born on a Monday, a day which Thais associate with the colour yellow.