Huge rally in Cuba marks May Day
President Raul Castro, who succeeded his ailing brother Fidel in February, is attending the celebrations. He did not address the crowds.
Raul Castro, 76, has introduced a series of reforms since becoming the leader of the Communist state.
But he has also made it clear that there will be no political reforms to the one-party system.
Creating 'softer system'
Raul Castro arrived in Havana's Revolution Square wearing his trademark general's uniform, but he did not make a speech.
Instead, there was a brief speech by the leader of the trade union movement and then the march got under way, the BBC's Michael Voss in Havana says.
Cuban authorities say that 500,000 people are taking part in the parade.
This is the second year in a row that Fidel Castro, now 81, has not been present.
He stepped down after failing to fully recover from a series of emergency operations.