BEIJING (Reuters) - The breakneck pace of growth in China's 10 trillion yuan ($1.64 trillion) investment trust industry is unsustainable and earnings risk drying up as the government steps up financial reforms that will change sources of revenue, research shows. Close to 90 percent of revenues in the industry are at risk in the long run with about 40 percent of earnings forecast to disappear completely in five years, according to a study by consultant McKinsey & Company and Ping An Trust. The sector, the second-biggest financial industry in China after banks, earns most of its present income from financing riskier borrowers and helping banks and other institutions buy assets that they cannot invest in due to regulations. But these revenue sources will vanish as China liberalizes its financial industry to let investors buy into a range of assets, and give riskier borrowers more access to credit, the research said. "Just how big a role will be left for trust companies and at what margins is unclear," the report said. To survive, China's trust firms will have to remake themselves into companies similar to Goldman Sachs, specializing in investment banking, private wealth management and alternative asset management, said Stephan Binder, a director at McKinsey. A part of China's ballooning shadow banks, investment trusts have exploded on the back of a class of borrowers who cannot borrow from banks due to regulations or their risk profiles. Trusts have stepped in to fill the void by linking borrowers to investors and savers seeking higher returns for their excess cash. Ping An Trust is a unit of the world's No. 2 insurer by market value, Ping An Insurance Group Co . ($1 = 6.0924 Chinese yuan) (Reporting by Koh Gui Qing; Editing by Jacqueline Wong)