Venezuelan president Hugo Chavez is hosting leaders from across the Americas at a two-day summit.
Mr Chavez described the new regional bloc that excludes the US as a tribute to his hero South American independence hero Simon Bolivar, saying the time has come to put an end to US hegemony.
“Only unity will make us free,” Mr Chavez said to applause at the opening ceremony. “This is the path: Unity, unity, unity!”
He called it an achievement that Latin America has been seeking for 200 years, and shouted: “Viva Bolivar!”
Nicaraguan president Daniel Ortega echoed Mr Chavez’s sentiments, saying Latin American and Caribbean countries should ensure that the policy of US intervention to protect the region’s nations, declared by President James Monroe in 1823, is never revived.
“We are sentencing the Monroe Doctrine to death,” Mr Ortega said.
The 33-nation Community of Latin American and Caribbean States includes every country in Latin America and the Caribbean.
Unlike the Washington-based Organisation of American States, or OAS, it will have Cuba as a full member and exclude the US and Canada.
Cuban president Raul Castro said that if it is successful, the creation of the new bloc known by its Spanish initials Celac will be “the biggest event in 200 years”.
“I’m sorry it isn’t Fidel who is occupying the place that I am, because he is the one who deserves it,” Mr Castro said of his elder brother, who permanently stepped down from Cuba’s presidency in 2008.
Mr Castro condemned this year’s Nato airstrikes in Libya as a crime and said Latin American and Caribbean nations should declare themselves a “territory of peace and free of foreign militaries”.
Other Latin American leaders said they see Celac as a forum to build closer economic and political relations across the region, but not as a platform for challenging US policies.
Mexican President Felipe Calderon said it will be a group “to work in favour of unity and prosperity”.
Colombian president Juan Manuel Santos, who is a US ally but also has friendly relations with Mr Chavez, said that “Celac isn’t being born to be against anyone”.