There are four basic signs of a stock bubble:
1. high levels of borrowing for stock purchases;
2. prices rising at a pace that can't be justified by the underlying rate of economic growth;
3. overtrading by retail investors; and
4. exorbitant valuation.
In 2015, the Shanghai market had reached the extreme end of all four bubble metrics which is rare.
The amount that Chinese investors borrowed to buy stock had set a world record, equal to 9% of the total value of tradable stocks.
Stock prices were up 70% in just 6 months, despite slowing growth in the economy.
On some days, more stock was changing hands in China than in all other stock markets combined.
In April 2015, the state-run People's Daily crowed that the good times were "just beginning."
In June 2015 the Shanghai market started to crash, and it continued to crash despite government orders to investors not to sell.