Argentine President Cristina Fernandez de Kirchner, Bolivian President Evo Morales and Uruguayan President Jose Mujica joined Maduro, 50, in paying respects to Chavez, who lay in a wooden casket at the military academy in Caracas -- his head and torso visible under a glass pane, and the lower half of the casket draped with the Venezuelan flag, The New York Times reported.
Chavez, 58, died Tuesday after suffering from cancer for nearly two years, the government said.
Officials in Washington said a members of Congress will join State Department officials in a U.S. delegation to Caracas, but there was no word on who would make the trip, The Washington Post reported.
Officials said there were no immediate plans for the United States to retaliate for Venezuela's expulsion of two U.S. military attaches at the U.S. Embassy in Caracas shortly before Chavez's death, the newspaper said.
Iranian President Mahmoud Ahmadinejad, who said Chavez will "return to Earth together with Jesus" and the Shiite Muslim figure Imam Mahdi, was traveling to Caracas Thursday.
The Los Angeles Times reported LA Philharmonic Music Director Gustavo Dudamel, a native of Venezuela, will fly to Caracas for Chavez's funeral, and may conduct a concert as part of the funeral. The newspaper said Dudamel was expected to return to Los Angeles for a Sunday concert.
The South American leaders who showed support for Maduro, a former bus driver and union organizer, then walked with him alongside the black hearse carrying Chavez's casket through the streets of Caracas, the capital.
The leaders were surrounded by hundreds of soldiers in green fatigues and tens of thousands of civilians wearing the national colors, yellow, blue and red.
When Chavez's body arrived at the military academy from the Carlos Aveledo Military Hospital 7 hours later -- a 5-mile trip -- it was piled high with flowers, caps and T-shirts thrown by the surging crowds, The Miami Herald reported.
Chavez -- whose career included a failed 1992 coup, a successful 1998 election campaign and then 14 years as the three-times re-elected president of the oil-rich nation -- is to lie in state until a state funeral Friday.
Maduro signed a decree calling for seven days of official mourning, as "Acting President of the Republic," the state-sponsored Correo del Orinoco newspaper reported Wednesday.
An Information Ministry spokesman said Maduro had not been sworn in yet. The spokesman told The Wall Street Journal he didn't know when the ceremony would take place.
A handful of lawmakers said rival Chavez loyalist National Assembly President Diosdado Cabello was constitutionally required to be acting president following Chavez's death until a vote is held.
The vote is to be held within 30 days.
Attorney General Cilia Flores, Maduro's wife, said on state television Maduro was rightfully in line to assume the interim presidency while an election is called.
"In the moment that [Chavez] disappears physically, immediately and automatically ... the vice president is in charge," she said.
She said her husband had the blessing of Chavez to lead the nation.
Maduro is widely expected to be the official candidate to succeed Chavez. Opposition leader Henrique Capriles, 40, who lost to Chavez in October's presidential vote, is expected to be the opposing candidate.
Many businesses remained closed Wednesday, partly out of mourning for Chavez and partly out of fear his passing could cause unrest, the Journal said.