Revelers -- many exiled by Havana's communist regime -- honked car horns, banged on pots and drums, and danced, cried, and waved Cuban flags in a crush of communal euphoria.
Castro died late yesterday, his brother Cuban President Raul Castro announced on national television around midnight.
In Miami -- home to the largest concentration of Cuban-Americans in the US -- the news spread quickly and with fervour.
"It's sad that one finds joy in the death of a person -- but that person should never have been born," said Pablo Arencibia, 67, a teacher who fled Cuba 20 years ago.
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Sensing the historic moment, younger revelers streamed the event on Facebook Live, posted pictures on Instagram, and broadcast the celebrations on FaceTime and Skype to friends and relatives on the island.
Little Havana and Hialeah -- Miami neighborhoods where many Cuban exiles settled -- saw people dance, hug, and exchange comments like "it took so long," and "now only Raul is missing."
"Cuba Libre" -- Free Cuba -- has been a rallying cry for exiles ever since the Castro brothers took over Cuba in 1959. The rum and Coke drink of the same name, however, predates the Castro regime.
The late-breaking news roused some out of bed to join the street party in pajamas.
Some sang the Cuban national anthem. Others shook up bottles of champagne and sprayed fizz among the revelers.
People of all ages gathered, mostly of Cuban descent, but also some Americans.
"It's a major moment for the Cuban community and I'm with them," said a retired Florida native named Debbie. "I live in Little Havana and this is a big part of our lives. The community always comes together here."
"He should have died a long time ago! He's a criminal, a murderer and a wretched being!" screamed 78-year-old retiree Hugo Ribas in a voice full of rage mixed with euphoria.
"The brother should have died too -- in that family they're all criminals!" added Ribas, who has been in Miami for four years.
"It took too long," said Cuban immigrant Analia Rodriguez, 23, who has lived in Miami for a decade.