South Korean stocks turned lower after starting a tad higher Thursday on tech losses after the downgrading of the US credit rating.

The benchmark Korea Composite Stock Price Index fell 10.85 points, or 0.41 percent, to 2,605.62 in the first 15 minutes of trading.

All three US major stock indexes finished lower Wednesday as investors took profits on monthslong gains after Fitch Ratings downgraded the US credit grade to AA+ from AAA for the first time since 2011, citing "repeated debt limit standoffs and last-minute resolutions."

Private payrolls increased more than expected in July, indicating continued labor market resilience.

In Seoul, big-cap tech shares drove the decline.

Market bellwether Samsung Electronics was flat, and No. 2 chipmaker SK hynix was down 0.92 percent.

Internet portal operator Naver lost 2.2 percent, and Kakao, the operator of popular mobile messenger KakaoTalk, retreated 1.13 percent.

Leading battery maker LG Energy Solution dropped 0.74 percent and its smaller rival Samsung SDI lost nearly 1.7 percent.

Top chemical producer LG Chem went down 0.93 percent.

Steel giant Posco Holdings sank 2.22 percent and its battery component-making affiliate Posco Future M plunged 2.57 percent.

Auto shares started in positive terrain.

Hyundai Motor gained 0.36 percent and its affiliate Kia advanced 1 percent. Hyundai Mobis, Hyundai Motor's auto parts affiliate, went up 0.66 percent.

Bio stocks also gained ground, with Samsung Biologics jumping 2.15 percent and Celltrion adding 1.28 percent.

The local currency was trading at 1,297.70 won against the US dollar at 9:15 a.m., up 0.8 won from Wednesday's close. (Yonhap)