Thousands have been paying their last respects to the sister of the King of Thailand, Princess Galyani Vadhana, BBC reported.
More than 2,000 Thai soldiers in dress uniform are pulling an elaborately decorated chariot carrying the princess's remains through Bangkok.
The body of the princess, who died 10 months ago aged 84, will be cremated on a 40m (130ft) high funeral pyre.
Correspondents say the $10m (?6.7m) funeral is intended to reinforce the monarchy's status in Thai society.
It is taking place at a time of intense political turmoil, in part fuelled by uncertainty over the succession of King Bhumibol Adulyadej, they add.
Anti-government protesters from the People's Alliance for Democracy (PAD) have also been occupying the main government offices for more than two months, with the aim of toppling the administration led by Prime Minister Somchai Wongsawat.
They claim Mr Somchai is a proxy for former PM Thaksin Shinawatra, who was ousted in a military coup in 2006.