Shares in mainland China have been suspended for a second time this week after markets plunged by 7% in just 30 minutes on Thursday.

Following huge losses in the summer, Chinese regulators implemented a new 'circuit breaker' system to suspend trading if shares fell by 7% in an attempt to reduce volatility.

The CSI 300 index dropped 7.2% just 30 minutes after trading opened on Thursday morning, triggering the halt and making it the shortest day of trading in China's history. The Shanghai Composite index fell slightly more at 7.3%, while the tech-focused Shenzhen Composite lost 8.3%.

Following the first suspension on Monday, it appeared that markets had started somewhat of a fightback on Wednesday, when the Shanghai Composite ended the day 2.3% above Tuesday's close.

The latest suspension of trading prompted the China Securities Regulatory Commission to ban major shareholders from selling more than 1% of a company's shares within three months of 9 January. A similar ban has been in place for six months, but that is due to expire on Friday.

Analysts say that investors are concerned by moves made by the Chinese central bank to weaken the yuan. The bank set its guidance rate against the US dollar to its lowest level since 2011. It suggests that China wants to boost exports - a sign that the country's economy is in fact worse that recent data has estimated.