Tunguska Event, If an Airburst happened near a major city what damage could occur?

I heard the Tunguska event is a 1 in a 100 year event. They say it was an Airburst from either a fragment of Comet or Asteroid about 5 to 10 Kms above the Earths surface releasing anywhere between 5-30 megatons of TNT energy. If it were to happen near a large city would it flatten a large area? Would they be able to discover and prevent another event similar to Tanguska in time to prevent it from possibly bursting above the Earths surface?