"Currently the information we have is six deaths and three wounded", the spokesperson said, declining for the moment to say whether the gunman was included in the toll.
The attack caused panic, with images on Twitter showing dozens of people fleeing the church.
The shooting occurred right after mass at the Metropolitan Cathedral in Campinas, a city about 60 miles north of Sao Paulo, according to Wilson Cassante, a spokesman for the archdiocese. Authorities said the shooter, a systems analyst with no criminal record, was not a member of the church.
"It was frightful", witness Alexandre Moraes told the GloboNews channel.
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Police in the plaza outside rushed in when they heard the shots, Ventura told a news conference.
The wounded were taken to hospital in Campinas.
One person said: "Whenever I'm in Campinas I get scared, so now I just know that a guy shot eight people in the cathedral and then committed suicide".
The gunman ran to the altar while firing at police and was hit in the side. He fell to ground and shot himself in the head, Ventura said.
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Gandolfo had 2 guns with 28 rounds left when he died. "Thanks to the intervention of police, something much bigger was avoided", said Ventura, adding that the four injured were in stable condition.
The incident took place at 1 pm local time (8.30 pm Indian time).
It was scary. He came in and started shooting randomly at people.
While Brazil had almost 64,000 murders past year, more than any other country, mass shootings in public areas are relatively rare.
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Bolsonaro has vowed to loosen gun laws, to allow Brazilians to arm themselves against criminals, a policy that many critics have said could only lead to more violence.