BHP Billiton said yesterday that growth in China, its most important customer, had “softened” during the three months ended September and warned “volatility and uncertainty” would continue in the short term.

The world’s biggest mining group delivered the downbeat assessment when issuing its quarterly production review. It showed strong gains in petroleum, iron ore, manganese and coal, compared with the previous September quarter, but declines in aluminium, diamonds and stainless steel materials.

China accounts for 20 per cent of BHP’s sales by value, and the rapid growth of its economy has underpinned the boom in commodities prices over the past five years.

Although BHP said its fundamental view on the outlook for China had not changed, the group said the country had “not been immune to the global slowdown”.

BHP said: “Macroeconomic indicators show that Chinese growth has softened during the quarter, albeit from very high levels. We expect volatility and uncertainty to continue in the short term.

“Notwithstanding this short-term uncertainty, we remain confident that the ongoing industrialisation and urbanisation of China and other developing economies will continue to drive stronger longer- term demand for our products.”

BHP added it had delivered a “strong” performance in the September quarter given a “challenging supply environment” characterised by disruptions such as hurricanes in the Gulf of Mexico. The group’s iron ore output during the quarter rose by 15 per cent to 29.8m tonnes, a record, following its expansion in Western Australia’s Pilbara region.

BHP’s London-listed shares closed down 9 per cent at 880p, amid falling mining stocks.

Shares in BHP and other leading mining groups, including its takeover target Rio Tinto, have plunged in the past two months in line with sharp drops in commodity prices on expectations of weaker global growth and reduced demand from China.