Looking on the internet deeply has found these results:

in an emergency is the most popular phrase on the web.

at an emergency 124,400,000 results on the web	in an emergency 165,700,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Or at least an emergency exit strategy? He was brought on duty here at an emergency. At the present time, it takes an average of three hours after the first symptoms of a heart attack are recognized by the patient, before that patient arrives at an emergency room. They shall be equipped with at least an emergency telephone and two fire extinguishers. Estes is at an emergency threat level briefing all day. At least in an emergency leave. So, would a terrorist organization want to black out the ability of police and fire to communicate at an emergency? I work at an emergency department in a different hospital.	What to do in an emergency 5. See the advice in 4 What to do in an emergency. My old man has a stash in Hong Kong for me to use in an emergency. and adopting necessary and justifiable measures to resolve specific problems in an emergency. A radio beacon crewmen can send to the surface in an emergency. In order to resolve specific problems, the Commission shall adopt implementing acts which are both necessary and justifiable in an emergency. Only use it in an emergency. Call the police in an emergency.

at an emergency

124,400,000 results on the web

in an emergency

165,700,000 results on the web

More popular!

Or at least an emergency exit strategy?
He was brought on duty here at an emergency.
At the present time, it takes an average of three hours after the first symptoms of a heart attack are recognized by the patient, before that patient arrives at an emergency room.
They shall be equipped with at least an emergency telephone and two fire extinguishers.
Estes is at an emergency threat level briefing all day.
At least in an emergency leave.
So, would a terrorist organization want to black out the ability of police and fire to communicate at an emergency?
I work at an emergency department in a different hospital.

What to do in an emergency 5.
See the advice in 4 What to do in an emergency.
My old man has a stash in Hong Kong for me to use in an emergency.
and adopting necessary and justifiable measures to resolve specific problems in an emergency.
A radio beacon crewmen can send to the surface in an emergency.
In order to resolve specific problems, the Commission shall adopt implementing acts which are both necessary and justifiable in an emergency.
Only use it in an emergency.
Call the police in an emergency.