Brazilian television reports that presidential candidate Eduardo Campos was killed when the small plane he was traveling on crashed in a residential area in the port city of Santos. (Reuters)

Presidential candidate Eduardo Campos died Wednesday when the small plane that was carrying him and several campaign officials plunged into a residential neighborhood in the Brazilian port city of Santos.

All seven people aboard the plane, including a campaign photographer and cameraman, a press adviser and two pilots, died in the crash, Santos City Hall press officer Patricia Fagueiro said.

She said six adults and a baby on the ground suffered non-life-threatening injuries, but rescue officials said later that five people were slightly hurt.

In a solemn address, President Dilma Rousseff declared three days of official mourning in honor of Campos and said she would suspend her campaign during that time.

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

Brazilian presidential candidate Eduardo Campos poses for a photo with a supporter, during a campaign rally in Osasco, Brazil. The PSB presidential candidate died Wednesday when the small plane that was carrying him plunged into a residential neighborhood in the port city of Santos, a City Hall official there said. (AP/AP)

Polls suggested he was running 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.

Rescuers stand next to part of the wreckage of the Cessna 560XL aircraft that crashed carrying the presidential candidate of the Brazilian Socialist Party (PSB) Eduardo Campos in Santos, Sao Paulo state, Brazil, on August 13, 2014. (Ricardo Nogueira/AFP/Getty Images)

It was not immediately clear whether Silva would assume Campos’ spot as the party’s presidential candidate. Under Brazilian law, in the event of a candidate’s death, a party has 10 days to decide on a substitute.