A line of mourners stretching some three kilometers queued to file past Campos's coffin, placed outside Recife's local government headquarters to allow people to say a final farewell.
Brazil President Dilma Rousseff was in attendance as ceremonies got under way with an open air mass.
Campos, 49, died when his campaign jet slammed into houses in Santos city in bad weather on Wednesday, killing all seven people on board and setting buildings alight.
A popular former governor of the northeastern state of Pernambuco, Campos was married with five children.
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Around 250 police officers were on duty for today's ceremonies.
Rousseff, who leads the polls for October's elections, was booed by sections of the crowd as she arrived for the mass.
Former President Luiz Inacio Lula da Silva and several ministers accompanied Rousseff.
Lula, a close friend of the family, wept as he embraced Campos's widow Renate after the mass, followed by Rousseff and the current second place presidential contender, Aecio Neves.