This is the story of one person who was extremely close to an exploding nuclear bomb. You would think it would be impossible to survive, if you are inly 300 meters from ground zero. But its not.

https://www.inicom.com/hibakusha/akiko.html

it should be explained that the atomic bombs in Japan (1945) were exploded in the air. but just the same, being almost directly underneath an explosion is an extremely serious incident. Nevertheless, survival is possible.

The current situation with N. Korea is being exploited for hysteria - especially by Kim Jong-Un himself. I doubt that N. Korea has this capability today. But it is better to take preventive action, hopefully through meaningful negotiations, before they do get this capability.