It's getting harder to predict metals consumption in China, the world's biggest user of raw materials, the billionaire CEO said in a phone interview in London. Glencore reported a 56 percent plunge in first-half profit on Wednesday and cut the earnings forecast for its trading division.

"At the moment none of us can read China," said the 58-year-old South African who's the second-largest shareholder in the company. "None of us know what is going on there and I'm yet to find the guy who can predict China correctly. China in the first half was a lot weaker than anyone expected."

Glasenberg, who ran a large part of Glencore's business with China from Hong Kong in the 1990s, is steering the company through the strongest headwinds since the Swiss commodity trader's $10 billion initial public offering four years ago. Glencore outlined further reductions in capital spending in its earnings report, and is reducing debt in an effort to maintain dividends while preserving an investment-grade credit rating.