China's 21 largest brokerage firms announced Saturday they would invest more than $19 billion in the country's stock markets in order to curb its precipitous fall over the last three weeks.

The brokers will spend at least 120 billion yuan ($19.3 billion) on so-called "blue chip" exchange traded funds (ETFs), the Securities Association of China said in a statement after an emergency meeting in Beijing.

The group promised to act "firmly" to stabilise local markets, after a spate of official policy moves to stop the sell-off.

The Shanghai stock market has plummeted by almost 30 percent over the past three weeks. On Friday the Shanghai Composite Index closed down 5.77 percent to end at 3,686.92 points.

Experts fear it could turn into a full-brown crash introducing even more uncertainty into global markets as Europe teeters on the edge of a potential exit by Greece from the eurozone.

The $19 billion investment represents 15 percent of the brokerages' combined net assets.

The firms said they would not sell the stocks they held on July 3 and would continue to buy more as long as the benchmark index remains below 4,500 points.

The move follows an announcement by the market regulator Friday to limit initial public offerings (IPOs) in an attempt to curb plunging share prices.

IPOs in China disrupt the rest of the market as official restrictions mean almost all of them go up 44 percent on their first day of dealings -- so investors drain existing holdings to try to secure the near-guaranteed profits.

The volatility is not linked to the ongoing crisis in Europe. Shanghai had swelled by 150 percent in the last twelve months and experts had expected a sharp correction.

China's Geely invests in Iceland methanol factory
Reykjavik (AFP) July 3, 2015 - Chinese group Geely, the owner of Swedish carmaker Volvo, said Friday it had become a major shareholder in an Icelandic company that operates the world's first renewable methanol fuel plant.

Geely said it would invest $45.5 million (41 million euros) over three years in Carbon Recycling International (CRI) and become a "major shareholder", but did not specify how much of the company it would hold.

The aim is to "collaborate on the deployment of renewable methanol fuel production technology in China and explore the development and deployment of 100 percent methanol-fuelled vehicles in China, Iceland and other countries," the two companies said in a joint statement.

Geely sees methanol as a replacement for petrol in its automobiles.

Geely chairman Li Shufu, in Reykjavik for Friday's announcement, reiterated that his group has a "long-term goal of zero emissions."

In March 2013, Geely began piloting methanol-fuelled vehicles, and in 2014 it became the first company in China to achieve mass production of methanol-fuelled vehicles.

CRI was founded in 2006 in Reykjavik and is a world leader in developing technology to produce renewable methanol fuel from clean energy and recycled CO2 emissions.

CRI has an annual production capacity of 4,000 tonnes of renewable methanol, marketed under the name Vulcanol in Europe where it is blended with gasoline and used for the production of biofuel.

CRI's plant is linked to the Svartsengi geothermal station in southwestern Iceland, whose surplus mineral-rich water fills up the Blue Lagoon, one of Iceland's most popular tourist attractions.

The plant emits very little carbon dioxide but what is emitted is in very concentrated form, which makes the transformation of CO2 into methanol financially viable, as opposed to a coal plant for example where the separation of CO2 and nitrogen is costly.

Iceland sees China as a key trading partner, becoming the first European country to sign a free trade agreement with Beijing in 2013.