Witnessing an accident can be a really daunting thing to deal with. The main thing to remember is the stay calm and do not panic.
 
Calling Emergency Services:
 
Witnessing an accident can be just as traumatic as being involved in one. Your instincts are likely to be telling you to help and while this is all very well, it’s important to be calm and collected.
 
Consider your own safety, as the last thing you want to do is cause another accident.
If you’re in a car, use your hazard lights to warn oncoming traffic of an incident.
Once at the scene, check to see who is injured and to what extent and call the emergency services.
Firstly you should try and get together all the witnesses and get any many people as you can to help.
If someone is trained in first aid get them to assist the injured until the emergency services have arrived.
Also try and keep onlookers back from the scene and make sure the scene is safe from any further incidents.
Make sure that someone speaks to the emergency services consistently so that they get all the information they need. It is best that the person on the phone is calm.
Looking after the injured: 
 
If there are people who are badly insured do not try not to move them unless it is dangerous to leave them where they are.
If you are skilled in first aid make sure that:
  • The airways are clear and they can breath
  • reduce bleeding by putting pressure on the wounds
  • Keep their circulation going by keeping them warm and elevating any injures.
If you are not trained in first aid the best thing to do is the leave the injured until the Emergency services arrive. Offering comfort and emotional support is the best thing that you can do.
After the Emergency services has arrived: 

 

You may be asked by someone involved in the accident or the police after the accident to give you name and contact details. This is usually to help who is investigating the accident.
You should make notes and write down a detailed account of what you saw before, during and after the accident. Also if you took photographs after the accident use these as well.