Federico Parra | AFP | Getty Images
An anti-government activist shouts slogans during a protest against the installation of the Constituent Assembly on August 4, 2017, in Caracas.
The assembly will function in the same downtown Caracas palace complex as the existing opposition-run congress, which could potentially be dissolved by the new all-powerful body.
The two bodies are expected to hold sessions in parallel, separated by an ornate cobblestone courtyard.
Governments ranging from Latin American neighbors to the United States and European Union have condemned the vote, with the Vatican making a last minute plea for authorities to suspend it.
Socialist Party officials converged on congress in a festive march in which they carried portraits of independence hero Simon Bolivar and Chavez, whose image was removed by the opposition legislators when they took over in January 2016.
“The constituent assembly is love, peace and loyalty,” said Raquel Rodriguez, a 57-year-old government worker who joined the march. “A lot of people have not been loyal to this (movement), but everyone here has.”
The delegates to the assembly sang the national anthem, led by a recording of the voice of the late Chavez.
The assembly’s election on Sunday prompted U.S. President Donald Trump to label Maduro a dictator, a term the opposition has long used to describe the unpopular leader.
Brazil on Friday recommended that Venezuela be suspended from trade bloc Mercosur until it returns to democracy.