China weighed in to the bidding battle for the world's minerals deposits yesterday when it launched a dawn raid to snap up a 9 per cent stake in Rio Tinto, the UK-listed mining giant at the centre of a takeover battle.

Chinalco, a state-owned mining company, in a joint exercise with Alcoa, the US aluminium group, spent $14 billion (€9.5 billion) in a move designed to block a planned $119 billion takeover bid from rival miner BHP Billiton. Together they secured up to 12 per cent in Rio's London-listed shares. This gives them a 9 per cent overall stake in Rio, which enjoys dual listing in London and Sydney.

BHP had been expected to launch an offer of three BHP shares for each Rio share on Wednesday, the deadline set by the UK Takeover Panel. But the Chinalco gambit threw BHP's plans into disarray. Marius Kloppers, its chief executive, will this weekend decide whether to plough on with the bid.

Chinalco president Xiao Yaqing said his group's acquisition of a stake in Rio was driven by a need to diversify outside China, its bullish outlook for commodity prices and "our belief in the fundamental value of Rio Tinto". The UK-listed firm owns some of the world's best iron ore, copper and aluminium mines and is a big supplier to China.

But people close to the deal said the primary motive was to make it more difficult for BHP to buy Rio. The Chinese government is dismayed at the prospect of a BHP takeover as it would give the combined company a virtual monopoly on iron ore supplies to China.