Bhumibol, who died at 88 two weeks ago, was adored by many of his subjects and seen as an anchor of stability in a kingdom rocked by turbulent politics.
His passing has thrust the country into a year of official mourning, with most Thais wearing only black and white since his death and TV channels devoting hours of airtime to footage from his 70-year reign.
But today was the first time the public has been allowed to enter the ornate throne hall where his body is lying in a coffin behind a gilded urn.
"I have been waiting here since 1:00 am," said Saman Daoruang, an 84-year-old sitting in a massive queue that snaked around a large field outside the palace, where tens of thousands were gathered by morning.
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Many of the black-clad mourners, who hailed from around the country, were seen wiping away tears as they left the spired building.
Like many in the crowd, Saman slept under a tent on the grassy parade grounds after arriving in Bangkok by train from northern Nakhon Sawan province.