What are the hardware and software tools required to import physical worlds into a game engine? Can I use a HD camera to do that? What do the popular game engines support?
Well, it's certainly nothing game-related, but it technically is possible to take multiple (2D) photographs of an object and use Photosynth to approximately recreate the object's 3D space. It's pretty neat, you should check it out.
Otherwise, there are 3D scanners but they are typically pretty small-scale. You certainly can't scan a large area with one of those.
There is also such thing as a stereo camera, or a camera with 2 (or more) lenses, which can therefore capture "3D" data. But I don't think these have progressed as far as being able to create 3D models out of the dual images they create, and even if they did, the models would only be from one viewpoint so they'd be incomplete just as Photosynth's are. I would think the latest 3D movies use stereo cameras when recording in order to capture this effect, but they could be using something else (a camera with a sonar attached or something, maybe).
The best thing to do is to create it from scratch. Take pictures of textures and unique objects (signs, etc.), take note of dimensions, and take whole-scene pictures for reference. Then have a 3D artist sit down and recreate it in 3D. Any automated large-scale 3D model creator, if one exists, would be wildly expensive.
Can I use a HD camera to do that?
To take the texture pictures, sure! I recommend a camera which is good at up-close shots.