Fireworks exploded over Havana Bay and five Cuban agents imprisoned in the United States sent greetings as ailing leader Fidel Castro turned 81 on Monday, spending his second consecutive birthday convalescing at an unknown location.

"Today we celebrate one more anniversary of the birthday of our Comandante en Jefe Fidel Castro, who turned 81 and who will continue celebrating many more birthdays with Cuba and the world," Havana resident Rosa Maria Suarez said in the early hours of Monday as she and hundreds of others stood on the Malecon sea front just after midnight to watch the fireworks marking Castro's birthday and the end of Havana's annual summer carnival.

"He's celebrating with his family at home, but it's as if he were with us here," said student Irane Neskaye, also watching the colorful pyrotechnics show popping over the bay with the skyline of Havana's Cabana Fortress in the background.

Two documentaries about the bearded revolutionary's life were scheduled to air on state television early Monday evening.

From prisons in the United States, five Cuban agents serving long terms on espionage related charges sent greetings of their own, which were published on Monday's Communist Party newspaper Granma.

"On this 81st birthday, we desire for you health and vitality, that you have many more, and that we can celebrate all those future anniversaries together in our beautiful fatherland," wrote Ramon Labanino, one of the so-called "Cuban Five" who were living in Miami a decade ago when they were arrested on espionage charges. The men deny they were seeking U.S. secrets and say they were gathering information about violent groups in an effort to prevent terrorist attacks against the island.

No major public celebrations of Castro's birthday were announced, and there was no expectation that he would make a public appearance more than a year after he announced he had undergone emergency intestinal surgery and was temporarily ceding power to his brother Raul, who is now 76. Even when well, Castro traditionally has celebrated his birthday in a low-key manner, often simply sharing a cake with Cuban school children.

Raul Castro, the longtime defense minister, in recent months has appeared to have consolidated his rule even though no procedural steps have been taken to make his role a more permanent one.

Life has changed little in Cuba in more than a year since the younger Castro assumed leadership of a caretaker government on July 31, 2006. Many believe Raul is more likely than Fidel to undertake modest economic reforms in the island's communist-run system, but no major changes are expected while the elder Castro is still alive.