The ChiNext Index, China's NASDAQ-style board of growth enterprises, opened 1.24 percent lower at 2,056.29 points.
A journalist, an official with China's securities watchdog and four senior executives of CITIC Securities, China's largest brokerage, were placed under "criminal compulsory measures" on Sunday for market manipulation and trading violations.
Since mid-June, China has rolled out a slew of measures to stabilize its volatile stock market, with a focus on pumping funds into the system.
Despite this, key indices have continued to nosedive over the last fortnight. This crackdown on illegal trading indicates that the government is diversifying its measures.