Rio Tinto reported a record $US7.6 billion ($A7.08 billion) first half net profit compared with the previous corresponding period, thanks once again to booming commodities markets, driven by industrialisation in Asia.

Global miner Rio Tinto says it is confident that demand for its main products of iron ore, coal and aluminium will double, despite the uncertain world economic outlook.

However, underlying earnings of $7.25 billion were slightly below analysts' expectations of around $7.48 billion.

Chief executive Tom Albanese said he was pleased with the first half profit after floods and cyclones sent production tumbling early in the year.

The company will pay an interim dividend of 54 US cents a share, up 20 per cent.

Rio Tinto increased its share buy-back program by $US2 billion to $7 billion, as had been widely expected, which is to be completed by the end of March 2012.

The company said first half net profit would have been $1.23 billion more had it not been for extra costs related to the weather disruption and higher production costs including labour.

"We were actually quite pleased with the quality of the result, particularly given the severe weather conditions we saw affecting volumes and to some extent costs in the first half," Mr Albanese told reporters.

"Our longer-term picture remains absolutely intact, we expect in the next 15-20 years consumption trends will lead to doubling in demand for iron ore, copper, aluminum and certainly other commodities.

"We remain positive for the remainder of 2011 and into 2012 ... it is this economic outlook that underpins our confidence to continue ramping up our investments in future growth."

Mr Albanese said important risks included a credit tightening in China and volatile sovereign debt problems leading to a financial crises in Europe.

The result was driven by Rio Tinto's cash-cow iron ore division that contributed about 80 per cent of the net earnings, lifting its performance by nearly 45 per cent to $U5.54 billion.

A combination of "surprisingly" high steel production and demand from China - where economic growth was 9.5 per cent - and an inability to bring new supply on stream could keep iron ore prices above $US100 a tonne, Mr Albanese said.

Rio Tinto is the world's second largest iron ore producer and is in the midst of a $629.6 million Pilbara expansion program to 333 million tonnes per year (Mtpa) by 2015 and expects to produce in excess of 240 million tonnes globally this year.

Rio Tinto spent more than $US5 billion ($A4.66 billion) in capital expenditure in the first half, including the acquisition of Mozambique-focused coal company Riversdale.

"We will focus on the best quality projects in the iron ore sector in WA, copper in Mongolia and coking coal Mozambique," Mr Albanese said.

Price movements boosted earnings in all of Rio Tinto's major commodities by nearly $US5 billion, including copper, molybdenum, gold and aluminium.

The company's energy groups, including coal and uranium, performed worse than analysts' forecasts, with underlying earnings of $US375 million, 39 per cent lower than the 2010 first half.

Adverse weather meant lower volumes and higher costs.

The stronger Australian dollar hurt earnings in US dollar terms, and uranium production declined 54 per cent with a processing plant in the Northern Territory shut from late January to mid June.

Rio Tinto released its results after the market closed in Australia, with its shares performing similarly to the overall bourse down $1.02, or 1.31 per cent, at $76.58 yesterday.

In early London trading, Rio Tinto was trading down 112 pence at £39.03 by 7.26pm (AEST) yesterday.

Originally published as Rio Tinto posts record profit