FLC OF AN MD11 OBSERVED A BALLOON OFF THEIR R WING DURING DEP CLB THROUGH 8300 FT MSL (5840 FT AGL) IN FOREIGN AIRSPACE.

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LOCATION: SAO PAULO DEP. WE DEPARTED RWY 9L AND TURNED TO THE 247 DEG RADIAL OFF OF BCO. WE WERE FOLLOWING THE TONI DEP; CLBING THROUGH 8300 FT MSL; AND WERE APPROX 5 MI FROM TONI INTXN. IT WAS MY LEG (CAPT) AND SUDDENLY NOTICED SOMETHING GLOWING RED AT APPROX OUR 12:30 O'CLOCK POS AND EITHER AT OR SLIGHTLY BELOW OUR ALT. I POINTED IT OUT TO BOTH THE FO AND FE AND WAS READY TO MAKE A L TURN IF NEEDED WHEN IT WENT OFF OUR R WING. WHEN WE WENT BY THE OBJECT; I NOTICED IT WAS A HOT AIR BALLOON THAT WAS UNDER 'FIRE.' THE FLAMES WERE THE ONLY THING VISIBLE FROM THE INITIAL OBSERVATION; BUT AS WE CLBED BY IT I COULD SEE THE ENTIRE BALLOON. I DON'T KNOW IF IT WAS MANNED OR NOT; BUT IT SURE COULD HAVE BEEN DISASTROUS TO BOTH US (CREW PLUS PAX) AND ALL OF THE OCCUPANTS OF THE BALLOON. OUR LATERAL DISTANCE FROM THE OBJECT COULDN'T HAVE BEEN MORE THAN 1000 FT -- AND MAYBE EVEN LESS. NOTHING WAS SAID FROM EITHER THE TWR OR DEP CTL REGARDING THE BALLOON'S WHEREABOUTS. I INSTRUCTED THE FO TO NOTIFY DEP TO RELAY THE POS OF THE BALLOON TO THE OTHER AIRPLANES DEPARTING GRU. I CAN'T IMAGINE BEING ABLE TO SEE AND AVOID THESE BALLOONS AT NIGHT IF THE BURNERS WERE NOT LIT. I HAVE NO CLUE AS TO WHY THEY ARE FLYING ON A DEP RTE AT NIGHT AT THE SAME ALT AS THE NUMEROUS AIRLINERS LEAVING GRU.