Retired Cuban leader Fidel Castro has made a rare public appearance by joining the opening session of the National Assembly.

Since falling ill in 2006 and ceding the presidency to his brother, Fidel Castro has given up all official positions except as a deputy in the National Assembly.

At today's session, he took his seat beside brother President Raul Castro, only the second time he has graced the assembly chambers since his illness and the first since 2010.

Fidel's surprise appearance added to expectations, fuelled by his brother, that the usually routine session might shed light on future leadership of the communist-run nation.

In a back and forth with reporters on Friday, Raul Castro joked about his eventual retirement and urged them to pay attention to the conclave, which is closed to foreign journalists.

"I’m going to turn 82. I have a right to retire already," he said.

The 612 deputies, who were elected in an uncontested vote 3 February, are expected to name a new 31-member Council of State with Raul Castro as president, despite his quip.

The National Assembly meets for just a few weeks each year and delegates its legislative powers between sessions to the Council of State, which also functions as the nation's executive through the Council of Ministers it appoints.

The new government is almost certain to be the last headed up by the Castro brothers and the generation that has ruled Cuba since they swept down from the mountains in the 1959 revolution that led to a long-running feud with Washington.

80% of the parliament's 612 members, with an average age under 50, were born after the Revolution.