Brazilian presidential candidate Eduardo Campos has been killed in a plane crash, local authorities say.

Mr Campos' private jet crashed in bad weather as it prepared to land in the coastal city of Santos, just south of Sao Paulo, the Sao Paulo state fire department said.

The crash killed all seven people on board.

The plane was en route from Rio de Janeiro's Santos Dumont airport to Guaruja airport outside Sao Paulo when it hit bad weather, according to aviation authority 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.

The air force said the plane was a private Cessna 560XL, a medium-sized jet.

Television images showed smoke billowing from the crash site in a residential area.

Officials said multiple people had been killed in the crash, but were unable to give a death toll because the fire was hampering access to the area.

"There are fatalities but we still do not have a number confirmed," a Sao Paulo state police spokeswoman said.

Santos firefighters said there were at least 10 people injured, according to Globo's online news portal G1.

Preparing for presidential poll

Mr Campos, the Brazilian Socialist Party (PSB) leader, was running third in opinion polls with the support of about 10 per cent of voters in recent polls.

Brazilian president Dilma Rousseff has cancelled all campaign activities for three days following Mr Campos' death, Ms Rousseff's Workers' Party said.

Brazilian presidential candidate Eduardo Campos speaks during a meeting at the CNI headquarters in Brasilia, July 30, 2014. ( Reuters/Ueslei Marcelino )

Mr Campos, 49, a former governor of north-eastern Pernambuco state, was running as a business-friendly leftist and had strong support from many banks and industrial groups.

His death could see Marina Silva, his running mate, become the Brazilian Socialist Party's candidate.

Ms Silva was not aboard the plane that crashed, a PSB source told Reuters.

She placed a strong third in the 2010 presidential election and enjoys robust support from young voters and evangelical voters, but her pro-environment agenda means that many in Brazil's powerful agribusiness sector distrust her.

Ms Rousseff is leading in polls with about 36 per cent of voter support. Mr Neves has enjoyed about 20 per cent support and was widely expected to face Ms Rousseff in a second-round runoff.

The presidential election is scheduled for October 5.

Brazil's main stock index lost as much as 2 per cent following initial reports that Mr Campos was on the crashed plane, but later pared losses to just over 1 per cent. The currency also lost ground.

Reuters/AFP

