Castro died on Friday at age 90, a decade after ceding control to his younger brother Raul Castro, 85.
Chants of "Viva Fidel!" resounded as tens of thousands massed in Havana's Revolution Square on November 29 evening to pay homage to Castro. "United, the people will never be defeated!" rang another.
Raul Castro embraced ideological ally, visiting Venezuelan President Nicolas Maduro, as the ceremony got underway.
The White House announced on November 29 Obama would not send a presidential delegation. Instead, the United States will be represented by Jeffrey DeLaurentis, chief diplomat at the US embassy in Havana, and Ben Rhodes, an Obama aide who represented the United States in 18 months of secret talks that led to detente.
Many leaders of Latin America's left, including Maduro and Bolivian President Evo Morales, flew in to attend the ceremony in the same space where Castro once delivered rousing, marathon speeches.
African leaders included Zimbabwe's Robert Mugabe and South African President Jacob Zuma, who paid Castro a tribute of his own. The late Nelson Mandela repeatedly thanked Castro for his efforts in helping overturn apartheid in South Africa.
Few leaders from the world's major powers are heading to the Caribbean island, with many sending second-tier officials instead.
China has sent Vice President Li Yuanchao, while Chinese President Xi Jinping visited the Cuban embassy in Beijing to pay his condolences, China's foreign ministry said
Russian President Vladimir Putin has skipped the ceremony but described Castro as a "true friend of Russia." The Kremlin said he held a different view on his legacy to that of Trump, who has called the Cuban leader "a brutal dictator."