I was able to see the event unfold while waiting in the hold block. It was an airbus, and they evacuated the a/c via the slides. All the equipment was there and the pax were all loaded into the people movers and taken back to the gate. We couldn't see exactly what the problem was, but a ramp agent said it was a brake fire. They towed the a/c clear of the runway and parked it in the hold block. We couldn't find out much more.