Underlying earnings rose 12% to US$4.9 billion, in line with analyst consensus, while half-year net earnings dropped 6% to $4.1 billion.

Net earnings of $4.1 billion included an $800 impairment on the carrying value of the company's interest in the Oyu Tolgoi copper mine in Mongolia, after it reported technical issues last month.

Underlying EBITDA was 11% higher year-on-year at $10.25 billion and the EBITDA margin was 47%, the highest in 10 years.

The company's dominant iron ore business contributed heavily to the result, with EBITDA of $7.5 billion, up 33%, and a 72% EBITDA margin.

Free cash flow of $3.9 billion was 35% higher than 2018 first half.

"Our world-class portfolio and strong balance sheet serve us well in all market conditions," Rio CEO J-S Jacques said.

"This, together with our disciplined capital allocation, underpins our ability to continue to invest in our business and deliver superior returns to shareholders in the short, medium and long term. Our delivery is in evidence today, with our record interim returns of $3.5 billion."

The return comprises an interim dividend of $1.51 per share, or $2.5 billion, as well as a special dividend of 61c, of $1 billion.

Return on capital employed was a record 23%.

Net debt stood at $4.9 billion, up from a modest net cash position at December 31, mainly reflecting $7.8 billion of cash returns to shareholders paid so far this year.

The results were released as the Australian market closed. Rio shares finished 1.1% lower at A$97.81.