10 April 1940 has remained in history as "the great panic day". The reason for this designation is the panic that spread through the population of Oslo, after the rumors of the British bombing of the capital had spread. Here you can see how the Oslo people rush out of town on foot, on bicycles, in trucks and buses. The clip is without audio.
This one of the many things I didn't know before. I can't find much about it on the web in English; Wikipedia says:
The same day [10 April 1940], panic broke out in German-occupied Oslo, following rumours of incoming British bombers. In what has since been known as "the panic day" the city's population fled to the surrounding countryside, not returning until late the same evening or the next day. Similar rumours led to mass panic in Egersund and other occupied coastal cities. The origins of the rumours have never been uncovered.
It's interesting that the rumours named Britain as the aggressor. Of course Germany bombing a city it already occupied wasn't particularly plausible, so given that the rumour existed it would have to attach itself to Britain. The Altmark incident (and the planned mining of Norwegian waters,
though I assume that was not publicly known as it was interrupted by the German invasion which was publicised shortly before the panic) might have suggested that the British were prepared to go further and attack Norway to achieve their own ends. I don't know much about airmindedness in Norway before the war (apart from the ghost flyers) either but in recent months civilians in two small, nearby nations had already suffered aerial bombardment, namely Poland and Finland (and let's not forget China and Spain in 1938) so to that extent the panic was not unreasonable.