Venezuela's opposition says it will not attend the swearing-in of Hugo Chavez's anointed successor as interim president.
Opposition spokesman Angel Medina says Nicolas Maduro's ascension is "a violation of the constitutional order".
Critics believe Venezuela's 1999 charter stipulates that the speaker of the National Assembly take power in the event of a presidential death.
Mr Medina also voiced concern that tonight's swearing-in ceremony is taking place at the same military academy where Mr Chavez is lying in state.
He says it sets a bad precedent because the military should play no role in politics.
The much-anticipated funeral promises to be a final turn on the world stage for the former paratrooper after 14 tumultuous years at Venezuela's helm.
Presidents and other dignitaries began arriving by mid-morning for the ceremony, and were still streaming in after the funeral's scheduled start, with no clear sign when the event might finally begin.
The Venezuelan government said more than 30 heads of state are expected to attend, from Iranian president Mahmoud Ahmadinejad to Cuba's Raul Castro, to the leaders of Mexico, Chile and Brazil.
US Representative Gregory Meeks, a New York Democrat, and former Representative William Delahunt, a Democrat from Massachusetts, represented the United States, which Mr Chavez often portrayed as a great global evil even as he sent the country billions of dollars in oil each year.
The Rev Jesse Jackson tweeted that he would be there, and Hollywood star Sean Penn also said he would attend.
"It is a great pain for us because we have lost a friend," Mr Ahmadinejad said on his arrival at the airport in Caracas. "I feel like I have lost myself, but I am sure that he still lives. Chavez will never die. His spirit and soul live on in each of our hearts."
Outside the academy, the line to see Chavez's body stretched more than a mile. Progress for those already waiting since the early hours was halted for the funeral, with some expressing impatience.
Government officials handed out water, and street vendors sold paper replicas of the presidential sash, which many people in the line slipped over their shoulder.
Elsewhere, the normally traffic-choked streets of Caracas were empty, with schools and many businesses shuttered. The government also prohibited alcohol sales. Many Venezuelans, particularly Chavez supporters, said they were caught up in the pomp and circumstance of the past few days, and flattered to be the subject of world attention.
Others said they were put off by what they saw as excess, particularly the plan to put Mr Chavez's body on permanent display.
Following the funeral, National Assembly speaker Diosdado Cabello is to swear in Mr Maduro as interim president, as Mr Chavez desired.