HAVANA -- Cubans went to the polls on Sunday to elect the members of the National Assembly of People's Power, who in turn will elect the nation's top leaders in April.

President Raul Castro, whose successor will be elected next month, was the first person to vote at 7 am at his local polling station in Segunda Frente, a town in the eastern province of Santiago de Cuba.

Castro is running for a seat at the assembly as a deputy representing his jurisdiction.

The First Vice President Diaz-Canel, who cast his vote in the central city of Santa Clara, 350 km east of Havana, said the elections were a way for Cubans to defend their political system and way of life.

"We are defending our (electoral) process, we are defending the revolution, which continues to be attacked amid a very complex juncture," he said, referring to the rollback in US-Cuba ties and the tightening of the trade embargo against the Caribbean island.

An engineer by training, Diaz-Canel has moved up the ranks of the Communist Party of Cuba (PCC) from serving as a local first secretary of the PCC to minister of higher education and now first vice president, a position he has filled since 2013.

Some eight million Cubans are eligible to vote for the 605 deputies of the National Assembly and 1,265 delegates to regional assemblies.

The National Assembly will be installed formally on April 19, when deputies will elect the new Council of State and its new president.