The Cuban flag has been proudly hoisted over Havana's newly restored embassy in Washington for the first time in 54 years.
The two nations restored diplomatic ties on Monday in an attempt to end decades of hostility.
In a historic ceremony attended by Cuban Foreign Minister Bruno Rodriguez, a large crowd cheered and shouted "Fidel, Fidel" and "Viva Raul" as the flag was raised by an honour guard.
They were referring to Cuba's revolutionary leader Fidel Castro and his brother Raul Castro, who is now the president of the communist-run Caribbean island.
After the US and Cuba officially resumed relations at one minute after midnight, an American official confirmed to AFP that US Secretary of State John Kerry will visit Havana on August 14.
He will be the first US secretary of state to visit Cuba since 1945, sealing what will be a major foreign policy legacy of President Barack Obama's eight-year tenure.
The historic turnaround between two bitter adversaries has come at breakneck pace after Obama and Raul Castro in December agreed to normalise ties.
The shift came after Washington acknowledged its policy of trying to affect change in tightly controlled communist Cuba through isolation and trade restrictions had failed.
At about 4:00 am (1800 AEST), the Cuban banner first took its place in the columned marble entrance hall to the State Department, hoisted between the flags of Croatia to the left and Cyprus to the right.
It was then raised at the embassy in Washington, which until Monday had been operating as an interests section.
At the US embassy in Havana however, where some 360 people including 30 Americans are employed, there were few outward signs Monday of its new status.
No US flag will fly over the building on Havana's waterfront Malecon until Kerry arrives.
US charge d'affaires Jeffrey DeLaurentis will stay in post in Havana until a new ambassador is confirmed, with his Cuban counterpart Jose Cabanas also staying in place in Washington.
In another historic move, Kerry was to formally receive his Cuban counterpart Bruno Rodriguez for talks Monday, before holding a joint press conference.