BHP Billiton, the world's biggest miner, reported an 86 percent drop in annual profit on yesterday amid plummeting commodity prices, as the company warned that China's slowing economy would lead to further market volatility. BHP saw a net profit of $1.9 billion for the 12 months to June 30, down from $13.8 billion a year ago, the company said. Revenue was down 22 percent to $52 billion. In response, the mining giant said it would cut costs, lowering its target for capital spending in the next financial year from $9 billion to $8.5 billion. Miners such as BHP are under increasing pressure as a slowdown in China's economy results in lower demand for key commodities such as iron ore and coal.