(Adds details, updates prices)
* Richemont falls after warning of challenging H2
* Syngenta rises on reports of possible DuPont deal
* Cement maker CRH rallies as UBS upgrades sector
* U.S. jobs data due at 1330 GMT
By Sudip Kar-Gupta
LONDON, Nov 6 (Reuters) - European stock markets were lower by midday on Friday, with luxury goods stocks among the worst performers after Richemont warned of tough times ahead.
Shares in Swiss agriculture company Syngenta rose more than 3 percent after media reports of a possible deal with DuPont.
The pan-European FTSEurofirst 300 index was down 0.46 percent and was set to end the week little changed, while the euro zone's blue-chip Euro STOXX 50 index fell 0.44 percent. Germany's DAX was down 0.19 percent.
Richemont fell 9 percent after the owner of the Cartier brand warned of a challenging second half after first-half net profits grew less than expected, as strong demand for high-end jewellery could not make up for weaker luxury watch sales in Hong Kong.
Richemont dragged down the shares of its rivals, with Swatch falling 6 percent and LVMH 4.6 percent.
According to data from Thomson Reuters StarMine, 52 percent of companies on the European STOXX 600 index have beaten or met market forecasts with their third-quarter results so far, while earnings guidance has been cut for the fourth quarter.
"Earnings have been very mixed so far. The European markets are looking quite sluggish at the moment, and I would be inclined to sell into any reasonable rally," said Berkeley Futures' associate director Richard Griffiths.
Cement maker CRH rose more than 4 percent after UBS upgraded the construction sector to "overweight" and named the Irish company as its preferred pick.
Many investors were also focusing on U.S. jobs data due at 1330 GMT for a sense of whether the U.S. Federal Reserve might raise interest rates next month.
Federal Reserve Chair Janet Yellen and New York Fed President William Dudley said this week the United States was ready for higher interest rates if upcoming economic data justified them.
The median forecast for October non-farm payrolls in a Reuters poll of economists is an increase of 180,000, above growth of 142,000 in September.
The FTSEurofirst and DAX are both up around 10 percent since the start of 2015, although both are also below their peaks for the year after signs of a slowdown in China, the world's second-biggest economy, knocked back markets in the third quarter.
Today's European research round-up (Additional reporting by Danilo Masoni; Editing by Toby Chopra)