* Chinese factory activity contracts at fastest pace since 2012
* Fed vice-chair to speak at 1 p.m. ET
* Google, Mattel to report after the close
* Twitter jumps after rumors of private equity deal
* Indexes down: Dow 0.77 pct, S&P 0.75 pct, Nasdaq 0.73 pct (Updates to open)
By Tanya Agrawal
Feb 1 (Reuters) - U.S. stocks opened lower on Monday, starting February on a dour note as weak economic data out of China exacerbated concerns about a global slowdown and oil prices resumed their downward spiral.
The data from China showed that the world's second-largest economy's manufacturing sector contracted in January at the fastest pace since 2012.
Oil prices fell after the China data added to worries about demand and an OPEC source played down talk of an emergency meeting to stem the decline. Oil prices have fallen more than 70 percent since mid-2014.
Slammed by collapsing oil prices that have fed doubts about the health of the global economy, stocks have had a volatile start to the year with traders expecting the Fed to scale back the number of rate hikes this year. Coming off the worst January since 2009, the S&P 500 is already down 5 percent for the year.
"Further weakness in China offers little evidence that their efforts to stabilize economic growth have been sufficiently effective and that would make a worry for commodity prices," said Mark Luschini, chief investment strategist at Janney Montgomery Scott in Philadelphia.
A 19-commodity Thomson Reuters/Core Commodity CRB Index , was down 1.5 percent. The index had hit a 13-year low in late January.
At 9:37 a.m. ET (1439 GMT) the Dow Jones industrial average was down 127.31 points, or 0.77 percent, at 16,338.99, the S&P 500 was down 14.58 points, or 0.75 percent, at 1,925.66 and the Nasdaq Composite index was down 33.58 points, or 0.73 percent, at 4,580.38.
Nine of the 10 major S&P sectors were lower, with the energy index's 2.2 percent fall leading the decliners. Oil majors Exxon and Chevron were down about 2 percent.
Wall Street surged over 2 percent on Friday after the Bank of Japan unexpectedly cut interest rates and technology shares rallied.
A slew of U.S. economic reports is scheduled to be released on Monday, including manufacturing and construction spending numbers.
The reports follow a weak reading of the GDP, which showed that the U.S. economy expanded at an anemic rate in the fourth quarter.
Data on Monday showed U.S. consumer spending was unchanged in December as households cut back on purchases of automobiles and unseasonably mild weather weighed on demand for utilities, but a jump in savings to a three-year high suggested there is enough muscle to boost consumption in the months ahead.
Investors will pay close attention to U.S. Federal Reserve vice-chairman Stanley Fischer's speech on the central bank's recent monetary policy at an event at 1 p.m. ET.
Fourth-quarter corporate reporting season is well under way, with S&P 500 companies on average expected to post a 4.1 percent drop in earnings, according to Thomson Reuters I/B/E/S.
Internet giant Alphabet, which reports after the close, was up 0.8 percent at $768. Toy maker Mattel will also release its quarterly reports after the close.
Chipotle Mexican Grill was up 5.1 percent at $476 after the Wall Street Journal reported that an E. coli outbreak that affected the burrito chain's customers last year may be declared as over as soon as Monday.
Twitter was up 5.2 percent at $17.68 after rumors of a private equity deal.
Declining issues outnumbered advancing ones on the NYSE by 2,218 to 562. On the Nasdaq, 1,744 issues fell and 571 advanced.
The S&P 500 index showed three new 52-week highs and two new lows, while the Nasdaq recorded seven new highs and 24 new lows. (Reporting by Tanya Agrawal; Additional reporting by Abhiram Nandakumar; Editing by Don Sebastian)