Cuba will change but not overnight: Obama

US President Barack Obama says Cuba will change after the communist-ruled island's rapprochement with Washington but not "overnight."

"It could happen fast," Obama told reporters on Friday. "It could happen slower than I would like."

But "it's going to happen and this change in policy is going to advance that."

But the US president, who co-ordinated with Cuban counterpart Raul Castro on the detente strategy that puts the former foes on track to normalise relations for the first time in more than half a century, dismissed the possibility of any immediate exchange of visits.

"We're not at a stage here where me visiting Cuba or President Castro coming to the United States is in the cards," Obama said in his final press conference of the year.

"There's nothing specific where we're trying to target some sort of visit on my part."

The White House, amid the flurry over Wednesday's announcement of the historic change in approach to Cuba, had signalled a presidential visit to Havana was not out of the question.

As part of the policy shift, Obama has ordered preparations to re-open its embassy and normalise ties, and consider lifting Cuba from the list of states that sponsor terrorism.

He also wants to eventually gain co-operation from Congress in lifting the 54-year-old US trade embargo on Cuba - sanctions that Obama described as "self-defeating - but acknowledged a congressional repeal would not be easy.

"We cannot unilaterally bring down the embargo," Obama said.

"There's going to be a process where Congress digests it. There are bipartisan supporters of our new approach, there are bipartisan detractors."

As for the changes likely to impact Cuba, "I think it will happen in fits and starts," Obama said.

"But through engagement, we have a better chance of bringing about change than we would have otherwise."