Supporters of rival presidential candidates clash in Sao Paulo, Brazil

Supporters of Brazil's two rival presidential candidates clashed in downtown Sao Paulo Thursday, as the race heats up ahead of Sunday's election runoff.

Brazil's leading G1 news service published an image of a street scuffle between supporters carrying the red flag of the ruling Workers' Party (PT) and its candidate, President Dilma Rousseff, and those holding the blue-and-white flag of the conservative Social Democratic Party (PSDB) and its candidate Aecio Neves.

"Flags from both parties were used as weapons in front of the Municipal Palace," G1 reported, adding no one was arrested and no injuries were reported.

The skirmish broke out after three buses carrying about 200 PSDB supporters arrived at a site near City Hall where some 40 PT loyalists were handing out leaflets and other campaign materials.

Members of the Metropolitan Municipal Guard intervened and broke up the fight.

Both parties issued statements afterwards, lamenting the incident and calling for calm in the lead up to Brazil's most contested presidential race in two decades.

Thursday's polls showed Rousseff with a six- to eight-point lead over Neves, though the candidates are close enough that a small portion of as yet undeclared voters could swing the vote one way or the other.