CLEAN : London attack: eyewitnesses tell of panic on bridge

A witness recounts a car crashing into parliamentary fencing, initially thought to be an accident, but later realized as a serious incident with gunshots. Emergency services and police quickly responded, cordoning off the area and evacuating people, including MPs. The public was shocked and panicked by the unfolding events.

What was the witness's realization about the seriousness of the situation?

How did the bystanders react to the incident?