And experts say it could take up to two days to put out the flames, which have been burning furiously since Saturday evening.
It broke out in a seven-storey building in the Cowgate area of the city, where there are lots of medieval buildings. It's listed as an important World Heritage Site by Unesco.
It's also a popular area for nightclubbers and tourists. About 150 people had to be evacuated from buildings nearby.
The blaze has caused millions of pounds of damage to more than 13 buildings and a firefighter has been hurt in the battle.
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