Defending champion Suzann Pettersen fired a second-round five-under-par 68 on the Blackstone Course at Mission Hills Resort on Friday to keep her lead at the World Ladies Championship.

The World No.2 golfer from Norway was sitting at 11-under-par at the halfway stage of the tournament, two clear of five other players.

Australian Nikki Campbell (67), England's Trish Johnson (68), South Koreans and So Yeon Ryu (67) and Ye Na Chung (69) and Valentine Derrey of France (68) were all on nine-under-par after a warm and overcast day in tropical Hainan.

Australian teenage amateur Minjee Lee started the day in a share of second place, one stroke behind the Norwegian, but shot 71 to fall four off the pace.

Pettersen's score card was flawless with four birdies on the par fives and another on the driveable par-4 16th, a dog-leg playing over a lake.

"Today was a little windy as we started," said Pettersen.

"Overall it was pretty decent. I feel like the par fives are playing like long par fours so five under today is certainly where I should be."

With some low scoring on the second day - including a career-best round of nine-under-par 64 from Italian Diana Luna - Pettersen felt that she would need to dig deep and produce some phenomenal golf to maintain her lead and successfully defend.

"You can really go low out here. There were a couple of really low ones out here today. It's impossible to say. I think you've got to be at least 16-under-par for the next two rounds; then I think you're in good shape."