The United States has authorised commercial ferry services to Cuba for the first time in more than a half-century, in a major step in improving relations between the two countries.

In what was hailed by ferry operators as an "historical event," the US Treasury on Tuesday lifted a decades-old ban and at least four Florida companies said they had been licensed to launch boat services to the island.

That adds to the charter air services that had been permitted until now, focused on enabling Cuban-Americans to visit their families.

The ferries will also be allowed to carry cargo to the communist island of 11 million, which sits just 150km off the southern tip of Florida.

Four companies confirmed they had received licences from the Treasury's Office of Foreign Assets Control to provide ferry travel.

Operators suggested the first trip would still take some time, because other permissions were still needed from authorities in both countries.

Turning point

In April, the presidents of the US and Cuba met in Panama City, marking a potential turning point in US relations with Cuba and the region after a decades-old blockade.

Barack Obama said after his meeting with Raul Castro that the discussions had been "candid and fruitful", and that a strong majority of citizens in both Cuba and the US would back warmer relations.

"I think our ability to engage, to open up commerce and travel and people to people exchanges is ultimately going to be good for Cuban people," Obama said at the Summit of the Americas in Panama City.

Castro had praised Obama as "an honest man" and said "every US president before him is to blame" for making Cuba suffer under long-held US sanctions.

A normalisation of relations has seemed unthinkable to both Cubans and Americans for generations.