Havana (Cuba) (AFP) - Cuban President Raul Castro steps down Thursday, passing the baton to a new generation in a transition that brings to a close the Castro brothers' six-decade grip on power.

"We have come a long way... so that our children, those of the present and those of the future, will be happy," Castro said in one of his last speeches as leader last month.

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The 86-year-old has been in power since 2006, when he took over after illness sidelined his brother Fidel, who seized power in the 1959 revolution.

Between them, father of the nation Fidel and younger brother Raul ruled Cuba for nearly 60 years, making the Caribbean island a key player in the Cold War and helping keep communism afloat despite the collapse of the Soviet Union.

On Thursday, that chapter of history will come to a close when the National Assembly elects a new president of the Council of State, catapulting the island into the post-Castro era.

- The chosen one -

The Assembly will begin gathering on Wednesday, although the vote itself will take place on Thursday, with members widely expected to select current First Vice President Miguel Diaz-Canel, a gray-haired 57-year-old who has climbed the party ranks and has been Raul Castro's right-hand man since 2013.

"There will be a sense of renewal, and there will be a sense of continuity," said Foreign Minister Bruno Rodriguez.

The outgoing president will remain at the head of the Communist Party until its next congress in 2021 -- when he turns 90 -- time enough to ensure a controlled transition and to watch over his protege when, inevitably, old-guard communists challenge his reforms.

Cuban political scientist Esteban Morales said the two would likely work in tandem, with Castro continuing to act as the ideological figurehead, while Diaz-Canel concentrates on the "very complex and difficult" task of running the government.

The heir to the Castros will be faced with modernizing the economy at a time when Cuba's key regional ally Venezuela, its source of cheap oil, is stumbling through an acute economic crisis, and amid a resurgence of the US embargo under President Donald Trump.