Brazilian presidential candidate Eduardo Campos died when the small plane that was carrying him and several campaign officials plunged into a residential neighbourhood in the port city of Santos, a City Hall official there said.
All seven people aboard the plane, including a campaign photographer and cameraman, a press advisor, as well as two pilots, died in the crash, City Hall press officer Patricia Fagueiro said.
In a statement on her official blog, Rousseff declared three days of official mourning in honor of Campos and said she would suspend her campaign during that time. "All of Brazil is in mourning," the statement said. "We have lost a great Brazilian."
Polls show Campos, the scion of a political family from the northeastern state of Pernambuco, was running in third place, trailing far behind Rousseff and another political rival. But his Brazilian Socialist Party ticket was widely regarded as among the best-placed to challenge Rousseff and her popular Workers Party, thanks largely to his running mate, the popular former Environment Minister Marina Silva, who joined Campos after she was prevented from running herself.
Silva's press adviser said that she was on the way to Santos, but it was not immediately clear whether she would assume Campos' spot as the party's presidential candidate. Under Brazilian law, in the event of a candidate's death, the party has 10 days to decide on a substitute.
Pundits were already predicting that Campos' death could complicate the presidential race for Rousseff.
Brazilian television broadcast a continuous loop of images of the wreckage, a smoldering pit in between buildings of several stories, with emergency response officials picking through the rubble. Brazil's top broadcaster Globo ran interviews with eyewitnesses who reported the plane was already ablaze before the crash that took place at around 10am local time (1am today, NZ time).
Aeronautical authorities said the craft, a Cessna 560XL, was attempting to land in bad weather.
It was not immediately clear whether anyone on the ground was injured in the crash, which reportedly at least partially damaged a gym, local media reports said. The plane took off from Rio de Janeiro, where Campos had appeared in a television interview on Tuesday, and was headed to the city of Guaruja, where he was to give a talk about Brazil's ports.
The country's top politicians expressed their shock and sorrow over the accident, with Vice President Michel Temer calling it a "tragedy for Brazilian politics."
"Eduardo Campos was a politician of principles and values," Temer wrote on his website. "Along with the entire country, I am shocked by this accident and by the loss for friends and family."
Eliseu Gabriel, a Sao Paulo city councilman who heads Campos' PSB in Sao Paulo, said the party has yet to make any decisions on how to move forward, saying only the campaign was "stopping" for the moment.
"The campaign was about to start, and he had a big chance of making it to the second round" of Brazil's two-round race, Gabriel said. "Eduardo Campos represented a great hope for a profound change in Brazilian politics."
As the initial shock of the crash passed, pundits began to speculate about how Campos' death would affect the October 4 presidential race.
David Fleischer, a political scientist at the University of Brasilia, told the AP that Campos' death was "bad news for Brazil and very bad news for Dilma."
Should Campos' running mate Silva assume the candidacy, she would likely pull votes away from Rousseff, forcing the race to go into a second round between Rousseff and the other main candidate, Aecio Neves of the Brazilian Social Democracy Party. Silva's support of Neves in a runoff could threaten Rousseff's chances of re-election, Fleischer said.
Rousseff, the hand-picked successor of popular former President Luiz Inacio Lula da Silva, has seen her popularity flag in recent months amid popular dissatisfaction with slowing growth, high taxes and poor public services — although she remained the strongest candidate. A survey by the Datafolha polling agency released Wednesday ahead of the accident showed 8 per cent of those questioned said they intended to vote for Campos, compared with 36 for Rousseff.
Campos, 49, was married and the father of five children, the youngest of whom was born in January. The heir of a political dynasty that stretched back to his grandfather, he served two terms as governor of Pernambuco state.
His brother, Antonio Campos, told Globo and other broadcasters that Campos would be buried in the family tomb in Pernambuco, where his grandfather's body lies. The grandfather, Miguel Arraes, died on the same date, August 13, nine years earlier.