BARCELONA (REUTERS) - Sun Yang eased into the final of the men's 800 metres freestyle on Tuesday as he continued his bid for a hat-trick of distance golds at the world swimming championships.

The towering Chinese matched a feat previously achieved only by Grant Hackett when he romped to the 400 metres freestyle title on Sunday, becoming only the second man after the Australian to claim world titles at 400, 800 and 1,500 metres.

While Sun's three titles have come at two different championships - he won the 800 and 1,500 in Shanghai two years ago and was second in the 400 - he is on course to match Hackett's three golds from the 2005 edition in Montreal.

"I feel good, the kind of feeling you always have in the preliminaries," Sun, gold medallist at 400 and 1,500 metres at last year's London Olympics, told reporters.

The 22-year-old said he was not thinking about breaking Zhang Lin's world record for the 800, which is not an Olympic event, which his compatriot set in Rome in 2009 with the aid of a now-banned non-textile suit.

Sun was second-quickest in the 800 heats on Tuesday behind Connor Jaeger of the United States, with Canada's Ryan Cochrane, silver medallist in Shanghai and third at the Rome world championships in 2009, third fastest.