* Weekly jobless claims rise
* Sept China factory activity falls
* Apple down 2.1 pct; biggest drag on the three indexes
* Indexes down: Dow 0.17 pct, S&P 0.20 pct, Nasdaq 0.62 pct (Updates to open)
By Abhiram Nandakumar
Oct 1 (Reuters) - U.S. stocks fell in early trading on Thursday as a sharp decline in Apple's shares weighed on the three major indexes.
Apple was down 2.1 percent at $107.9 at 10:06 a.m. ET, erasing opening gains for U.S. stocks.
Global markets were upbeat after data from China was not as bad as feared and investors awaited a barrage of U.S. data.
Factory activity in China shrank again in September, leading some investors to believe that the government will be more aggressive in its measures to boost the health of the world's second-largest economy.
Global investors will be looking to put a bruising quarter behind them - U.S. stocks posted their worst quarter in four years, while the Shanghai stock market plunged about 25 percent.
"Historically, the third quarter tends to be a difficult quarter and the fourth quarter tends to be the best quarter of the year," said Randy Frederick, managing director of trading and derivatives for Charles Schwab in Austin, Texas.
Investors will be parsing data released this week, with the crucial non-farm payroll numbers due on Friday, for clues on the timing of an interest rate hike by the U.S. Federal Reserve.
Data showed the number of Americans filing new applications for jobless benefits rose modestly last week.
Other data scheduled for Thursday includes Markit's final manufacturing PMI data for September at 9:45 a.m. ET (1345 GMT). The index's preliminary reading came in at 53 earlier this month.
The Institute for Supply Management's index of U.S. factory activity, to be reported at 10:00 a.m., is expected to have fallen to 50.6 in September from 51.1 in August.
General Motors, Ford Motor and the U.S. operations of Fiat Chrysler Automobiles NV were up slightly after they reported a jump in September sales on Thursday.
"I think there's reason for optimism, but at the same time, I think there are plenty of reasons to be cautious," Frederick said, adding that an increase in interest rates would be an "upside catalyst" for markets at the end of the year.
Crude oil prices rose to around $49 per barrel as Syria tensions escalated, countering further signs of an economic slowdown in Asia and rising U.S. inventories.
At 9:44 a.m. ET the Dow Jones industrial average was down 28.26 points, or 0.17 percent, at 16,256.44, the S&P 500 was down 3.85 points, or 0.20 percent, at 1,916.18 and the Nasdaq composite was down 28.42 points, or 0.62 percent, at 4,591.75.
Eight of the 10 major S&P sectors were lower, with the technology index's 0.9 percent fall leading the decliners.
San Francisco Fed Reserve President John Williams is scheduled to speak on the economic outlook at 2:30 p.m. in Utah.
Celgene was up 1.9 percent at $110.20 after J.P. Morgan raised its rating on the stock to "overweight" from "neutral".
Dunkin Brands sank 10.7 percent to $43.78 after company gave weak full-year forecast and said it would shut 100 stores.
Sarepta surged 15.22 percent to $36.75 after the biotech company said data on its drug for progressive muscle-wasting disorder showed long-term effectiveness.
Advancing issues outnumbered decliners on the NYSE by 1,781 to 868. On the Nasdaq, 1,115 issues rose and 1,066 fell.
The S&P 500 index showed 3 new 52-week highs and three new lows, while the Nasdaq recorded seven new highs and 27 new lows. (Reporting by Abhiram Nandakumar in Bengaluru; Editing by Saumyadeb Chakrabarty)