"I am convinced that if this threat is not stopped in West Africa with an immediate international response it could become one of the gravest pandemics in human history," said Castro, who is sending 461 Cuban doctors and nurses to West Africa.
He spoke in an address to six presidents or prime ministers from the leftist ALBA bloc of Latin American and Caribbean meeting in Havana, where they pledged to join forces to prevent Ebola from spreading in the Americas and to find ways to aid West Africa.
The foreign leaders praised Cuba's contribution to the fight against Ebola in West Africa. The communist-ruled island of 11 million people has committed the largest medical contingent yet of any single country to the front lines of the epidemic in Liberia, Sierra Leone and Guinea, where the hemorrhagic fever has killed more than 4,500 people since March in the worst outbreak on record.
No Ebola cases have yet been reported in Latin America or the Caribbean but the virus, which is spread through direct contact with the bodily fluids of infected people, has reached the United States and Spain.
The ALBA summit came together quickly after a Liberian man died from Ebola in Dallas on October 8.
Castro reiterated Cuba's willingness to set aside its 55 years of hostility with the United States, which is sending up to 4,000 military engineers, medical personnel and other troops to the region, to stand together in the anti-Ebola fight.
"Cuba is willing to work side-by-side with all countries, including United States," said Castro, who took over for his ailing older brother Fidel Castro in 2008.
United States has welcomed Cuba's aid, with US Secretary of State John Kerry highlighting the contribution of Cuban medical professionals.
The summit brought together the presidents of Cuba, Venezuela, Bolivia, Nicaragua and Haiti, the latter a specially invited guest.
They were joined by the prime ministers of Saint Lucia and Saint Vincent and the Grenadines. ALBA members Ecuador, Dominica, and Antigua and Barbuda sent senior officials, as did the United Nations, the World Health Organization and the Pan American Health Organization.
Cuba imposes strict requirements on travelers coming from the affected countries of West Africa, holding them for at least 21 days of observation before allowing them to travel freely in the country. Some 28 people have been held at a hospital in Havana, its director said on Friday.
Cuba's aid to the West African countries hardest hit by Ebola is the latest example of its long tradition of medical diplomacy. Havana has sent medical brigades to disaster sites around the world since the 1959 revolution that brought Fidel Castro to power.
Cuba also sends doctors overseas in exchange for money or goods, notably Venezuelan oil, making professional services a top export earner. More than 50,000 Cuban medical personnel are posted in 66 countries.