Choi closed her first round with four consecutive birdies and Korda had five birdies in the first eight holes en route to a four-stroke lead. Neither had a bogey on the day.
Stacey Lewis, Park Hee-young and Seo Hee-Kyung each turned in 5-under 68s to tie for third while eight players, including world No. 1 Inbee Park, are at 4-under 69.
Korda opened Thursday's play with a birdie and added two more at Nos. 3 and 4. Birdies at 6 and 8 allowed her to make the turn at 5-under. She had back-to-back birdies twice -- at Nos. 12-13 and then at 16-17 -- on the second nine for her 64.
Choi was 4-under on her first nine, with birdies at the second and third holes and again going back-to-back at Nos. 8 and 9. She pushed to 5-under with a birdie at 11 and jumped up the leaderboard by closing with birdies over 15-18.
Lewis and Park, who had birdies in the final three holes, were both bogey-free in the first round. Seo was just 1-under through 10 holes after three bogeys, two birdies and an eagle at the par-5 ninth. She, like Choi, closed the round with four straight birdies.
The tournament, officially called the Reignwood Pine Valley LPGA Classic, is the first of a series of LPGA events in Asia.