Shares in London-listed mining companies soared yesterday after rumours swept through the market that Rio Tinto, which is fending off a takeover attempt from rival BHP Billiton, could make a bid for Anglo American, the South African platinum producer.

Mining stocks were also supported by rising commodity prices and news that state-owned Aluminium Corporation of China, known as Chinalco, and its US partner Alcoa, had agreed to raise its stake in Rio to more than 14% from 12%. Rio's shares are listed in Sydney and London.

According to a memo dated January 30, Chinalco and Alcoa had agreed to buy up to 14.9% of Rio Tinto this month and had up to $24bn to spend.

The document, a copy of which was included in a filing by Rio to the Australian Stock Exchange on Wednesday and later obtained by Reuters, was signed just ahead of the Chinese and US firms' $14bn (about £7bn) investment in 12% of Rio's London-listed shares.

Just before BHP made an all-share offer on February 6, Chinalco said it "currently" had no intention to acquire more shares, but it has since declined to say whether it might buy more.

It has also reserved the right to counterbid for Rio Tinto.

Chinalco has created a special purpose vehicle company (SPV) in Singapore with the intention of acquiring additional shares, the memo states.

The document, dated January 30, gave a 30-day deadline for reaching the 14.9% stake.

Meanwhile, Rio would not comment on the rumours involving Anglo American but there has been persistent speculation in the City that the South African firm is a bid target of one or more rival miners.

Mining industry analysts said Rio could scupper BHP's takeover bid by acquiring Anglo American. Rio chief executive, Tom Albanee, has sent out signals to the City recently that the company is on the acquisition trail.

Anglo American shares rose 69p, or 2.2%, to £30.94 while stock in Rio jumped by 1%, or 55p to £55.55.

On Wednesday, Rio said its net profit for the calendar year 2007 slipped 1.7% to $7.3bn, the first decline in its annual earnings since 2003. But underlying profit was $7.4bn, up 1.4% on 2006.

The result was above analysts' forecasts for an underlying profit of between $6.9bn to $7.1bn.

Elsewhere in the sector, Xstrata, the UK-Swiss copper and nickel producer, is being stalked by Vale, the Brazilian-based iron ore company, which is believed to have offered about $80m (£40m).

However, Xstrata's board is said to have rejected the £40-per-share cash-and-shares bid from Vale and to be holding out for £45 per share.

The offer values the miner at about £39bn, deemed nowhere near enough by the board and Swiss-based Glencore, which owns 35% of Xstrata.

Xstrata's shares rose 1.9%, or 72p to £38.52p. Other miners also performed strongly. Platinum miner Lonmin was a beneficiary of takeover talk and higher commodity prices, rising 79p, or 2.4% to £33.59p.

BHP Billiton added 24p, or 1.6%, to 1566p while Vedanta Resources gained 50p, or 2.6%, to £20.04.