Image copyright Getty Images Image caption China's market regulator has introduced a string of new rules to try to relieve pressure on Chinese shares

Mainland Chinese shares rebounded on Thursday after regulators took further steps to try to calm the stock market.

The Shanghai Composite index reversed earlier losses to close up 5.76%, its biggest percentage gain since 2009.

A move to ban big investors from selling stocks may have helped to support the market, analysts said.

Meanwhile, the state-run news agency Xinhua said police were investigating "vicious short-selling" on the country's stock market.

Xinhua said authorities would "crack down" on operations that had broken the laws and regulations related to trading.

The benchmark Shanghai index closed up 202.14 points at 3,709.33.

Relieving pressure

China's market regulator has introduced a string of new rules in the past week to try to relieve pressure on Chinese shares. The Shanghai Composite has fallen by more than 30% since mid-June.

On Wednesday, the Shanghai Composite fell as much as 8.2%, leading some analysts to describe the session as 'Black Wednesday'.

In the latest efforts to try and stem the falling markets, Beijing has relaxed lending rules - making it easier for people to borrow money for investment - in the hope that they will buy more stocks. That follows a move late on Wednesday to ban investors holding stakes of more than 5% in companies from selling shares in the next six months.

Meanwhile, about 1,300 firms have halted trading in their stocks to prevent the value of their businesses falling further.

Analysis: John Sudworth, BBC News, Shanghai

The latest measure to be unveiled by the Chinese regulator is a ban on investors who hold more than 5% of any stock from selling it for six months.

It is an extraordinary restriction, but coupled with all the other government-backed efforts to shore up prices in the face of China's massive slump, it may have finally brought some stability.

That said, around half of all listed companies have voluntarily suspended trading, so it could be argued that the market is, in effect, as much seizing up as it is stabilising.

Analysts are divided over the extent to which the dramatic unwinding of China's massive lending-fuelled stock market boom poses a threat to the wider economy.

Why the volatility in Chinese markets?

China media: Negative market sentiment 'exaggerated'

Image copyright Getty Images Image caption Shares in Japan were down on Thursday as investors worried about China's stock market and Greece

Elsewhere in Asia

The volatility in China was echoed in Hong Kong, with the benchmark Hang Seng index reversing earlier losses to close up 3.73% at 24,392.79.

Japan's Nikkei 225 index reversed earlier losses to close up 0.6% at 19,855.50.

"Tokyo markets have been affected by Chinese shares since yesterday," said SBI Securities' Hideyuki Suzuki, who is general manager of the firm's investment market research arm.

"But the Hang Seng Index and red chips which are now in positive territory are giving [a] sense of relief," he said.

In Australia, the S&P/ASX 200 index ended flat at 5,470.97, while South Korea's benchmark Kospi index closed up 0.6% at 2,027.81.