A man has been seriously injured at the Pike River Mine site after getting trapped under a building.

The man was pinned under a partially collapsed building known as the bathhouse which was being moved by the new owner of the mine site.

The incident happened just before 9am.

The man was freed by colleagues and taken to Greymouth Hospital with moderate injuries.

A Solid Energy spokesperson said they're in the process of selling surplus equipment and the injured man wasn't a Solid Energy employee.

The site will remain shut down until a WorkSafe investigation's been completed.