If there is a bubble in the Chinese economy, some recent defaults on corporate debt there will be worrying. From the Business Insider,
For the past few years, China's companies, banks, and local governments have been loading up on debt.
Loans to companies and households stood at a record 207% of gross domestic product at the end of June, up from 125% in 2008, data compiled by Bloomberg shows.
If that doesn't worry you, consider that Greek debt is "only" 185% of GDP. ("Normal" debt for a country is somewhere around 100% of GDP.)
Corporate debt in China has grown faster than in any other top-15 economy.
Here's the chart:
Addendum: I had meant to add this when I posted this clip. I wonder to what extent there is a serious moral hazard problem in Chinese corporate finance: people lend to the corporations expecting the gubmnt to bail out the firms.
Addendum #2: see this about China's big PC maker.