Mourners wept as the funeral procession carrying his casket snaked through the streets to a cremation ground next to the palace where he was crowned king when he was teenager in 1941, Voice of America reported.
Sihanouk died Beijing Oct. 15 of a heart attack at the age of 89.
The cremation, the pinnacle of the seven days of mourning, will occur Monday.
Sihanouk aligned with the vicious Khmer Rouge after he was ousted in 1970, only to later be imprisoned by the regime. He eventually fled to China.
When the Khmer Rouge fell in 1979, Sihanouk led an insurgency against the Vietnamese-installed government and later returned to the Cambodian throne. He abdicated in 2004, making way for his son to become king.
Canons in formation along the banks of the Mekong River fired shells provided by Vietnam as the chariot carrying the king's coffin rolled by, The New York Times reported.
"It reminded me of the battlefield," said Mey Thorn, a bicycle rickshaw driver in Phnom Penh watching the procession. "Things are better now, getting better and better."
Sihanouk was eulogized as the father of the nation who built factories, schools, roads and hospitals.
"He is the father of integrity and the father of national unity," one government official said. "He is the best king ever."