As of right now, 90% of China's entire stock market is frozen. It's absolutely a 1929 style disaster. Were the authorities not stepping in constantly, the carnage would be far worse already - which is another way of saying, eventually it will get there no matter what they do.
That led to some bizarre circumstances, where new IPOs during the upside mania were going up by the limit every day for weeks after the IPO.
If you're comparing apples to apples (first few weeks of the American crash of 1929 to the current Chinese crash) the numbers look very similar.
There is no severe immediate risk of a depression in China. Their stock market is relatively very small compared to their economy as a whole and Chinese firms as a whole are nowhere near as dependent on it for raising capital as in western countries. Therefore the ammount of damage any fall in the stock market can do to the Chinese economy is fairly low.
The Chinese leadership has staked a lot of it's credibility and prestige on the rises in the stock market, as evidence of it's good economic management. As a result they, and anyone wantign to curry favour with them, were hyping up the market and blowing air into the bubble as hard as they could. Bad mistake. They'll learn.
"The market would not return to the peak closing of September 3, 1929 until November 23, 1954."
Minus that spending, it's not clear what would have happened, since we never had a return to the old status quo. The military investments of the war motivated the early development of Silicon Valley - thus, we'd be looking at a present day where "somewhere else" might have gained the tech hub crown.
That said, the current moment is one where the premises could change again. China has a strong and growing influence in the world, just as the U.S. did coming into the Depression. The particular circumstances differ, but a broad "cycle of empire" is one way to interpret things.