A Natural disaster is an event caused by natural processes of the Earth, such as earthquakes, floods, hurricanes, or volcanic eruptions, leading to widespread damage and loss.
A National disaster is a disaster (which can be natural or human-made) that is so severe and widespread that it overwhelms the response capabilities of local and regional authorities, requiring significant intervention and resources from the national government. It often involves a formal declaration by the national government.
The key difference is that natural disaster refers to the origin (natural phenomena), while national disaster refers to the scale and impact within a country, often leading to a national declaration, regardless of its origin.