Trading on the mainland Chinese markets was suspended for the day after shares plunged more than 7% for the second time this week. The mainland benchmark Shanghai Composite index also fell 7.3% while the tech-heavy Shenzhen Composite lost 8.3% before trading was stopped.The circuit breaker rule, a mechanism introduced to stem volatility in the market was triggered in the first 30 minutes of trading. Investors are nervous after the central bank moved to weaken the yuan.After the trading halt, China Securities Regulatory Commission announced that major shareholders could not sell more than 1% of a company's shares within three months as of 9 January.