Brazilian presidential candidate Eduardo Campos has died after a small plane carrying him and several campaign officials plummetted into a residential neighbourhood, throwing the October election into disarray.

All seven people onboard the plane, including a campaign photographer and cameraman, a press advisor, and two pilots, died in Wednesday's crash in the port city of Santos.

All of Brazil is in mourning. We have lost a great Brazilian. Brazilian President Dilma Rousseff

"The plane was trying to land, it aborted the landing and that's when the control tower lost all communications with the plane," Al Jazeera's Gabriel Elizondo said, reporting from the scene.

"Ten homes were affected; six people on the ground injured."

Eyewitness Sergio Martins told Al Jazeera: "At the moment it crashed we felt a big shake, it was an explosion and we didn't know what was happening, we thought a building had collapsed."

In a statement on her official blog, Dilma Rousseff, Brazil's president, declared three days of official mourning in honour 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."

Campos, 49, was a former governor of northeastern Pernambuco state, and had the support of about 10 percent of voters in recent polls.

Race turned upside down

The scion of a political family from the northeastern state of Pernambuco, he had been an ally of Rousseff but broke away ahead of the campaign for the October 4 presidential election.

That 10 percent support put him in third place, 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 Workers Party, thanks largely to his popular running mate, former environment minister Marina Silva, who joined Campos' ticket after her attempt to run for president herself failed.

"This completely turns the entire presidential race upside down," Al Jazeera's Elizondo said, adding that there was talk that Silva could now become the party's candidate.

Senator Aecio Neves, the centrist candidate running in second place, said he was "immensely saddened."

Silva was not aboard the plane that crashed. 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.