More than two dozen companies in China are postponing initial public offerings and security companies are pledging more than $19 billion for a fund to stabilize the country's free-falling stock market.

The 28 companies, which had obtained permission from China's securities watchdog for IPOs planned in Shanghai and Shenzhen, said they would postpone them due to recent market fluctuations and refund money already paid, the official Xinhua News agency announced late Saturday. That followed reports that regulators were asking companies to postpone the IPOs.

Twenty-one Chinese securities companies, in a joint statement released Saturday, said they would pledge no less than 120 billion yuan ($19.33 billion) to invest in Chinese stocks and funds. The securities companies also said they would continue to invest in the market as long the Shanghai Composite index, the Chinese equivalent of the Standard & Poor's 500 index, remains below 4,500. ıt closed at 3,686 on Friday. The statement was posted on the website of the Securities Association of China. The Chinese stock market has been in free-fall for three weeks, losing 28 percent of its value since June 12. Despite the plunge, the market is up 79 percent in the last year. The drop has wiped out several trillion dollars in market value in a matter of weeks.

Even though China is the world's second-largest economy, the Chinese stock market remains largely isolated. Foreign investors can only indirectly participate in the market through funds or through specialized brokerage services. Unlike the U.S. and European markets where institutional investors play a major role, the Chinese stock market is dominated by individual investors.

In the first half of the year, the Shanghai stock market led the world in initial public offerings: 78 companies issued shares in Shanghai, raising $16.6 billion, according to a study by the accounting firm EY. Hong Kong was No. 2 with 31 deals that raised $16 billion. Shenzhen was No. 5 with 112 deals that raised $7 billion.