Han hits six birdies to lead in Indonesia
Japan's Hideto Tanihara retained a share of second place after a three-under round, one stroke behind Han's total of 135.
Thaworn Wiratchant of Thailand, Michael Wright of Australia and Kiwi Michael Hendry, the defending champion and first-round leader, also hold a share of second.
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Hide AdLocal favourite Rory Hie (138) finished on two-under after birdies on his final three holes and is tied for sixth.
Han, the 19-year-old leading Order of Merit player in the field, holed six birdies to go along with a bogey to put himself in contention.
"I holed a lot of putts today as I got a feel for the greens," Han said. "If I can maintain that feeling I won't be far away come Sunday."
Former Ryder Cup player Paul McGinley (143) shot a three-under round to move up to 45th place. The Irish veteran started the day tied for 83rd after a two-over 74 in the first round.
McGinley recently recovered from a left knee injury that has hampered his play for most of the year.