Heres a link to the website. Its really quite interesting how they do it.
From the website:
First they replace the support pillars at ground level with computer-controlled metal columns. Then, a crew carefully demolishes the entire floor by hand, leaving the structure resting on the mechanical pillars, which then go down slowly until the next floor is at ground level. They replace the support pillars again with the mechanical ones, destroy that floor, and repeat the operation until they get rid of all the floors.
This makes it look as if the building is shrinking in front of you, or being swallowed by the street. According to the company, this method greatly reduces the environmental impact of the demolition, as well as the time. Kajima says that it speeds up the task by 20%, while making it easier to separate materials for recycling, as well as reducing the amount of products released into the air.