The world's third-largest mining company, Rio Tinto, has forecast higher prices for its core commodities of iron, alumina and copper after delivering a record first-half profit.

Net profit for the six months to June 30 climbed by 112.5 per cent on the corresponding period the previous year, to $US6.91 billion ($A8.01billion), underpinned by higher prices and production, particularly from iron ore.

Underlying profit, or earnings before interest and tax, rising 55 per cent to $A6.34billion, was broadly in line with analysts' forecasts.

Rio Tinto is reaping the rewards from the rapid urbanisation of China and other developing nations that has been driving greater demand for commodities and rising commodity prices for the past seven years.

Chairman Paul Skinner said, ''We expect prices for Rio Tinto's major commodities to remain substantially above the long-run trend in 2009.''

Shares in Rio Tinto, the focus of a hostile $A174billion takeover proposal from rival BHP Billiton, gained $A1.76, or 1.44 per cent, to $A124.06.

Earnings before interest, taxes, depreciation and amortisation for the half climbed by 73 per cent to $A13.23 billion. Rio Tinto's iron ore division was the group's biggest earner.

Underlying earnings for the iron ore division grew by 161.8 per cent to $A3.34 billion.

Rio Tinto chief executive Tom Albanese said, ''The outlook for iron ore remains excellent.''

He said Chinese demand for aluminium continued to grow strongly.

Rio Tinto, the world's second-largest aluminium producer, posted a 145 per cent increase to $A1.15billion in underlying after its Alcan acquisition last year.

Mr Albanese said the company was on track to deliver annual synergies after tax of $A1.28 billion from the end of 2009, higher than the initial estimate of $A696million.

Underlying earnings for Rio Tinto's energy division, comprising coal and uranium assets, grew 83.5per cent to $A787.34 million. AAP