Order an evacuation of the possible impact area; put emergency services on alert; divert flights…
Edit: this is something that is being practiced:
https://cneos.jpl.nasa.gov/pd/cs/pdc17/day2.html
Order an evacuation of the possible impact area; put emergency services on alert; divert flights…
Edit: this is something that is being practiced:
https://cneos.jpl.nasa.gov/pd/cs/pdc17/day2.html