Hjorth, who led by one after the first round, carded a 5-under 67 to join Kerr at 12-under-par 132. Il Mi Chung posted a 66 to move into third place at minus-11.
Nina Reis (68) and Seon-Hwa Lee (67) share fourth place at 10-under-par 134. Erica Blasberg, Sophie Gustafson and Young Kim are two strokes further back at minus-8.
Lorena Ochoa, who stands on atop the tour's money list, shares ninth at 7-under-par 137. The Mexican was even-par through 12 holes with a birdie and a bogey. Ochoa birdied the fourth and seventh to end at minus-7.
Women's world No. 1 Annika Sorenstam, who was paired with Ochoa for the first two rounds, is one stroke further back at minus-6 and she is tied for 12th. She birdied the 10th, but gave that stroke back as she bogeyed the 16th for the second day in a row.
Sorenstam atoned for that error with a birdie on 17. Around the turn, she climbed the leaderboard with birdies on four, five and eight.
Kerr started on the back nine and knocked a sand-wedge to 12 feet at the 10th. She rolled in that putt, then chipped to 2 feet at the 12th and knocked that in to move to minus-6.
The 28-year-old birdied the 14th, then drained a 35-footer for birdie on 16. After four straight pars around the turn, Kerr sank a 7-foot birdie effort on the third.
Kerr, who was paired with Ochoa and Sorenstam, came right back on No. 4 as she got up and down for birdie from right of the putting surface. She collected back-to-back birdies from the sixth to move to minus-12.
'I didn't hit it very well on Thursday, frankly,' stated Kerr. 'I've been working on some things with my coach and that helped my ball-striking today. I putted well too.'
Hjorth got off to a fast start with birdies on one and two, both from inside 8 feet. She got up and down for birdie on the par-5 fifth, then drained a 15-footer for birdie on No. 5.
The Swede missed the green at the par-3 seventh and tripped to a bogey that dropped her to minus-10. Hjorth traded a birdie for bogey from the 12th.
Hjorth got back to minus-11 thanks to a birdie on the par-4 14th. She dropped her approach 6 feet from the cup at the 17th and converted that birdie try to join Kerr in the lead.
'I did not hit the as well today as I did on Thursday,' Hjorth admitted. 'But I also made a few putts that were a little bit longer. I'm really looking forward to going out there with a share of the lead. It's going to be fun.'
Ochoa was joined in ninth by Kyeong Bae and Julieta Granada. Sorenstam shares 12th with Angela Stanford, Lee Ann Walker-Cooper, Tracy Hanson, Brittany Lang and Annie Young.
The cut line fell at 1-under-par 143 with 70 players moving on to the weekend. Among those missing the cut was 2005 champion Pat Hurst.