A corporate pilot reported numerous apparent hobbiest launched balloons of substantial size in the vicinity of SBGR and encountered at altitudes between 1000 MSL and 10;000 MSL.

Narrative

There seems to be a routine of launching very large; artistically designed balloons on weekends around Sao Paulo; Brazil. These balloons [can] loft as high as 10000 FT MSL; and above.Fortunately it was VMC and we were diligent about looking outside on the morning we conducted the PIRA5 STAR into SBGR. On that occasion we had to steer around two of these substantial airborne hazards that were directly on the arrival course at approximately 9000 & 7000 FT MSL. Still appalled by those encounters; one week later we witnessed another balloon about 1000 FT above the airport just as we were given takeoff clearance. That sighting heightened our vigilance to be aware of additional balloons during climb-out. And what a hazard rich environment we found! We witnessed no less than 8 more balloons on departure- all around the airport from 1000 AGL to 10000 MSL; and several on or within a few hundred feet of the CGO1 SID course. The balloons are probably approximately 10'x10'x10' and typically trail banners about 20 FT long. They look to be very detailed works of art.ATC seemed to have very little concern for these hazards and; of course; had no way to track them. I was told at our hotel in Sao Paulo that there is an artist community that builds and launches these craft. Apparently; designing them with some altitude limiting feature; much less coordination or consideration of air traffic safety is beyond their ability. I do not know how early they begin launching but even less than 1 hour after sunrise we encountered them as high as 7500 FT above the city.