What is the immediate priority action upon arriving first at the scene of a serious road traffic accident with injured persons?

1. Immediately pull victims out of crushed vehicles by their arms
2. Photograph the scene for social media before contacting authorities
3. Offer food and hot beverages to unconscious casualties
4. Secure the accident site (turn on hazards, wear vest, set up warning triangle) to prevent further collisions, then alert emergency services (112/127/129)