Aluminum Corp. of China and Alcoa Inc. bought a 7.2 billion pound ($14 billion) stake in Rio Tinto Group in a surprise attempt to derail BHP Billiton Ltd.'s hostile takeover bid for the world's third-largest mining company.

Rio surged in London after Chinalco, as the state-owned company is known, and Alcoa paid 21 percent more than the closing price yesterday. Chinalco, China's largest aluminum producer, and Alcoa, the No. 3 maker of the metal, bought an estimated 9 percent stake in Rio Tinto Group, spokeswoman Christina Mills said in an e-mail response to questions.

Chinalco opposes BHP's $119 billion proposal to acquire London-based Rio because it would create a company with too much power over prices as the supplier of a third of the world's traded iron ore and the biggest maker of aluminum and energy coal. Alcoa Chief Executive Officer Alain Belda helped establish Chinalco's listed unit by buying a stake in 2001.

``It's clearly a spoiling move,'' Tim Barker, who helps manage and advise on $54 billion of assets including BHP and Rio at BT Financial Group, said in Sydney. ``Where you've a blocking stake like that it would be difficult to win some aggrieved shareholders unless they thought they were getting the right deal.''

Rio gained as much as 793 pence to 5,749 pence and traded up 733 pence at 5,689 pence as of 11:57 a.m. on the London Stock Exchange. That's still short of the 6,000 pence a share price Chinalco and Alcoa paid for their stake. BHP advanced 138 pence, or 9.3 percent, to 1,615 pence.

Largest Acquisition

The purchase, China's largest overseas acquisition, was made through Shining Prospect Pte., a Singapore-based investment vehicle owned by Chinalco. Alcoa contributed $1.2 billion in funding to Shining Prospect to buy a 12 percent stake in Rio's London-listed shares, the companies said in the statement. The two companies reserved the right to make a bid should another party made a firm offer. Rio is listed in the U.K. and Australia,

``Chinalco takes up the most part of the 12 percent,'' Chinalco's Vice President Lu Youqing said in an interview by phone from Beijing. ``Rio Tinto is an international multimetal mining company, which fits with our development goals.''

Chinalco will consider increasing its stake dependent on returns achieved, Lu said.

Rio Tinto became the world's biggest aluminum producer last year, leapfrogging Alcoa, when its $38.1 billion takeover offer for Canada's Alcan Inc., trumped Alcoa's hostile bid.

Ultimate Breakup

``It is likely Chinalco, Alcoa and the Chinese government are aiming for an ultimate breakup of Rio Tinto,'' Michael Rawlinson, head of mining, resources and energy at Liberum Capita Ltd. in London, wrote in a report. ``This could be an opportunity to liberate attractive assets that Alcoa missed out on. China is short low-cost alumina and aluminum.''

BHP is considering options for its proposal to buy Rio, said Illtud Harri, a BHP spokesman in London.

The purchase reinforces that the BHP bid undervalues Rio, Mills said in London. ``We have had many calls since BHP's approach in November, but we have not engaged with anyone.''

BHP's three-for-one share offer for Rio was rejected in November. Melbourne-based BHP, the world's largest mining company, has until Feb. 6 to make a formal bid for Rio Tinto or shelve it for six months.

``It might stall or slow the whole BHP offer,'' said Mark Pervan, a senior commodity strategist at Australia & New Zealand Banking Group Ltd. in Melbourne. ``It might make them think twice as now there's a major shareholder that would be looking to extract full value.''

Beijing Visit

Rio Tinto's Chief Executive Officer Tom Albanese visited Beijing on Jan. 25 meeting Chinese clients and government officials. Luo Jianchuan of Beijing-based Aluminum Corp. of China Ltd., the publicly traded unit of Chinalco, in November said he was ``worried'' about BHP's bid for Rio.

Chinese steelmakers, the largest buyers of iron ore, and the government are studying a joint bid for Rio, an official at Chinese steelmaker Shougang Corp. said Dec. 4.

``Money is not a problem for Chinalco,'' said Zhang Xi, a Hong Kong-based analyst with UOB-Kay Hian Ltd. ``It must be backed by the Chinese government.''

China has been scouring the world for resources. Chinalco of China bought Peru Copper Inc. for $860 million last August, Anshan Iron & Steel Group in Sept. agreed to a A$1.8 billion ($1.6 billion) Australian iron ore joint venture, and Cnocc Ltd. in 2006 spent $2.7 billion buying Nigerian oil fields.

Chinalco's stake purchase dwarfs the 36.7 billion rand ($5 billion) that Industrial and Commercial Bank of China Ltd. agreed to pay for a 20 percent stake in Standard Bank Group Ltd. last year, then the largest overseas acquisition.

Rio hired Morgan Stanley, Macquarie Group Ltd., Credit Suisse Group and NM Rothschild & Sons Ltd. BHP is being advised by Goldman Sachs Group Inc., UBS AG, Citigroup Inc. Deutsche Bank AG, Sydney-based Gresham Advisory Partners Ltd. and JPMorgan Cazenove Ltd.