Cubans will no longer need an exit permit to travel abroad from January, the communist regime said on Tuesday, in a major overhaul of a half-century-old policy despised by the island's citizens.

The changes are the latest in a series of gradual reforms implemented in recent years by President Raul Castro, who took the helm from his ailing brother Fidel Castro in 2006.

Cubans will no longer have to apply for a "white card" to leave the island from January 14, and the period allowed for overseas stays will be extended from 11 to 24 months, according to decrees published in the official journal.

A bureaucratic headache, Cubans are required to show a letter of invitation from a relative or friend abroad and a visa from the destination country to get the permit, costing up to $500 in a country where monthly salaries average $19.

While Cubans will only need a passport from January to travel, the government indicated that it would continue to impose some limits to avoid a "brain drain" that it blamed on the United States.

The official daily Granma said Cuba will keep measures "to defend itself" as long as "'brain theft' policies aimed at taking away human resources essential to our country's economic, social and scientific development continue."

Cuba has pressed the United States for years to stop granting automatic residency to Cubans who set foot on US soil.

Despite travel restrictions in place since the 1960s, Cubans have emigrated illegally in droves, often using rickety boats to embark on dangerous sea voyages to nearby Florida.

Around two million Cubans have left the country in the last half century. The population today stands at 11.2 million.

The foreign ministry said the latest changes "take into account the right of the revolutionary state to defend itself against interference and subversion by the US government and its allies."

"For this reason, measures will be maintained which are aimed at preserving the human capital created by the revolution from the plunder of talent by the more powerful (countries)," it said.

Under the new rules, people who play "vital roles" in the country, such as soldiers, engineers, doctors and athletes, will need authorization from their superiors in order to get a passport.

The government also said a passport can be denied to Cubans who have a criminal record or a government debt, or for "national security and defense" reasons.

Cuban opposition blogger Yoani Sanchez, who says she was denied exit permits 20 times, voiced doubt that she would be allowed to travel when the changes take effect.

"My friends tell me no to get my hopes up with the new 'migration law,'" she wrote on Twitter. "They tell me I'm on the 'black list.' But I will try."

Cuban exile groups in the United States cautiously welcomed the changes.

"In principle... it is good news for Cubans so that they can begin to have a little bit more freedom," Omar Lopez Montenegro, human rights director of the the Cuban American National Foundation (CANF), told AFP.

But he added that "a passport is something that must be given freely to everybody," noting that "there are requirements that remain unclear."

Exiles also want to know whether Havana will allow Cubans to freely return to their home country.

Though a "white card" can be extended 10 times, Cubans must return to the island after it expires or lose the right to reside in Cuba.

Raul Castro announced last year that the government was planning immigration reforms that would be introduced gradually.

The president has pressed for economic reforms over the past two years aimed at modernizing Cuba's state-dominated economy while maintaining one-party rule.

The regime has been in crisis since the end of the Cold War and the demise of the Soviet Union, once its biggest patron. Today the nation relies heavily on the leftist government of oil-rich Venezuela for support.