Couple of things that makes this scary.
Since the Western banks tanked the market, China has been the "Engine that Could"; growth and demand in China has helped float the world economy's boat.
China has told people to relax, figuring on 7% growth this year. Outside analysts have downplayed that figure, saying 4-5% is more likely.
No matter how low it goes, that slowdown reduces demand for resources which in turn constricts the economic growth potential of resource economies.
How bad the downturn actually becomes is an open question; China's economic data is pretty opaque, so if there is a train wreck in the offing, we will have no clue until we are sorting the rubbish.
On the other hand...