Hong, one of 12 players in the field this week from the Korean LPGA, stands at 9-under-par 135 through 36 holes.
First-round leader Joo Mi Kim faltered to a 1-over 73. She was joined in second place by Karine Icher (71) and amateur Mi Jung Hur (70) at 5-under- par 139.
Paula Creamer (72), the highest ranked player in the field at world No. 7, shares fifth place at minus-4 with Suzann Pettersen (71), Jeong Jang (72) and defending champion Jee Young Lee (73).
Hong was steady over the opening nine holes. She rolled in an 18-foot birdie putt on the par-4 second to move to 5 under. Hong made the turn at minus-6 thanks to her second birdie in two days on the par-5 eighth at Mauna Ocean Golf & Resort.
She birdied the 10th for the second straight round to keep moving up the leaderboard. Hong kicked in a 3-foot birdie putt on the 14th, but gave that stroke right back with a three-putt bogey on 15.
Hong atoned for that error as she birdied the 16th to get back to minus-8. She closed with a 3-foot birdie putt on No. 18 to extend her lead to four after two rounds.
'I was just trying to have a good time. I was lucky to have a good score,' Hong said through a translator. 'This is my first time playing in an LPGA event and, rather than feel pressure to win the event, I want to enjoy it.'
Kim tumbled out of the lead as she struggled on the front nine. She bogeyed the fourth and double-bogeyed No. 5 to slide to minus-3.
The 20-year-old began to fight back with birdies on six and seven. Around the turn, Kim got back to even-par for her round with a birdie at 11.
However, she tripped to another double-bogey on the 14th. Kim collected her final birdie on the par-4 17th to end in a share of second.
Icher posted two birdies and two bogeys on the front nine. On the back nine, she wrapped birdies at 14 and 16 around a bogey on 15 for a round of 71.
Hur made a run late in the round to gain a share of second. She birdied the first and third, but bogeyed No. 2. Hur fell to minus-2 after a double-bogey at the fifth. After eight straight pars, she ran off three birdies on a four-hole span from the 14th to end at minus-5.
Hee-Won Han, who won her second event of the year last week at the Honda LPGA Thailand, stumbled to a 1-over 73. She is alone in ninth at 3-under-par 141.
Gloria Park, who shared third place at this event in 2003, is tied for 10th at minus-2 with Candie Kung and Patricia Meunier-Lebouc.