Global miner Rio Tinto reported a record second-half profit on Thursday, more than double a year earlier, matching forecasts as its biggest customer, China, snapped up iron ore, coal and copper.

It promised to return $5 billion to shareholders through a share buyback by the end of 2012 and increased its final dividend 20 percent above its earlier commitment, topping market expectations.

It said that commitment would still allow it to take advantage of future growth opportunities that might arise.

Underlying earnings before one-offs rose to $8.22 billion for the six months to December from $3.73 billion a year earlier, against analysts' forecasts around $8.29 billion.

Rio Tinto's shares have jumped 29 percent over the past year, far outstripping an 8 percent gain in the broader market as commodity prices have soared.

(Reporting by Sonali Paul; Editing by Ed Davies)