Brazilian presidential candidate Eduardo Campos died when his campaign jet slammed into houses in Santos city in bad weather, killing all seven people on board and setting buildings alight.
Campos, a 49-year-old socialist who had been running third in opinion polls for the October election, was flying to Sao Paulo to record a TV segment when his Cessna 560XL came down, breaking into pieces and igniting a large fire after impact.
President Dilma Rousseff, who is standing for a second four-year term, declared a state of national mourning and suspended her campaign for three days.
"All of Brazil is in mourning. We lost a great Brazilian today, Eduardo Campos. We lost a great comrade," the leftist president said in a statement.
Campos, a popular former governor of the northeastern state of Pernambuco, was married with five children, the youngest just six months old.
His plane was en route from Rio de Janeiro's Santos Dumont airport to Guaruja airport outside Sao Paulo, according to air force spokesman Pedro Luis Farcic.
"As it was preparing to land, the plane fell due to bad weather. Air traffic control then lost contact with the aircraft," he said.
All seven people on the plane died, the air force said.
In addition to Campos, the plane had two pilots, two advisors, a photographer and a videographer aboard.
Pieces of the destroyed aircraft were strewn around the crash site in a bustling residential neighbourhood of Santos, a port on the Atlantic about 75 kilometres from Sao Paulo.
A view of homes that were damaged by the crash. Photo / AP
Flaming piles of rubble sent up a large column of smoke, and several houses were on fire.
Santos restaurant owner Thiago Fernandes said the impact of the crash had shattered the front windows of his business.
"I was working in the restaurant and there was a very loud boom, like nothing I had ever heard. All the front windows broke," he told Globo News TV.
The air force said it had launched an investigation into what caused the medium-sized jet to crash.
- Platform of change -
Campos had been running with eight per cent support, according to a survey released on July 22 by polling firm Ibope ahead of the October 5 first-round election.
Rousseff leads the race with 38 per cent, while social democrat Aecio Neves has 22 per cent, the poll found.
Campos had been campaigning on a platform of change after 20 years of government by Rousseff's Workers' Party (PT) and Neves's PSDB.
He had been traveling to Sao Paulo, the Brazilian financial hub, to film a campaign-related TV segment with his running mate, ecologist Marina Silva, Globo TV reported.
Silva made a brief, emotional statement after the crash.
"This is a tragedy that brings us great sadness that I know the Brazilian people share," she told journalists, saying she and Campos had fought for "the hope of a better world."
The White House was among those to send condolences.
"We were deeply saddened" by the news, National Security Council spokeswoman Caitlin Hayden said in a statement.
Neves also cancelled his campaign events, saying he was "immensely saddened" by the loss of a friend, while former president Luiz Inacio Lula da Silva, whom Campos served as science and technology minister, said the country "has lost a public servant of rare and extraordinary quality."
Campos's PSB party said their presidential candidate had died "at the height of a brilliant political career."
The crash throws the party into uncertainty.
If it picks Silva to replace Campos, she could still conceivably mount a serious challenge for the presidency.
The popular former environment minister, who was born in a rubber-tapping town in the Amazon and only learned to read at 16 years old, came third in the 2010 presidential race with 19 per cent of the vote, running on the Green Party ticket.
Opinion polls earlier in the year found that if she ran again she would beat Neves to claim second place in the first round, before losing to Rousseff in the runoff on October 26.
The election uncertainty weighed on the Sao Paulo stock market, which tumbled two per cent after the crash but battled back somewhat to close 1.53 per cent down.