* STOXX 600 down 1 pct
* Tech sector falls 1.6 pct
* Chipmakers STMicro, Infineon, ams tumble
* Sodexo drops on downgrade
* Mediaset jumps after Sky deal (Updates prices, adds details, quotes)
LONDON, April 3 (Reuters) - European stocks tumbled on Tuesday as investors entered the second quarter in a febrile atmosphere of trade tensions and mounting pressure on big technology companies.
The pan-European STOXX 600 fell 1 percent, while Germany's DAX declined 1.4 percent, with industrials, financials and healthcare stocks the biggest weights.
The tech sector dropped 1.6 percent, weighed by chipmakers after an overnight report that Apple plans to replace Intel chips in Macs with its own.
The index has fallen 8 percent in the past three weeks as anxiety grew over big tech companies with the focus on Facebook's use of data, and regulation of Amazon.
Reports of Apple increasingly going down the "insourcing" route have dented shares in Apple suppliers around the world, most notably Europe's Dialog Semiconductor which has shed more than 60 percent in the past year.
On Tuesday, STMicro led fallers, down 3 percent, while ams declined 2.7 percent and Infineon fell 2.4 percent.
Risk appetite was poor across the board, as European investors followed U.S. and Asian investors to the exit after China retaliated against U.S. tariffs.
"We believe that risk-reward for stocks has not turned medium-term negative, and would be adding at these levels," wrote JP Morgan strategists in a note.
Equities have again entered "oversold" territory, they said, adding, however, that headwinds for technology stocks were increasing.
Outside the tech sector, food services group Sodexo was the worst-performer on the STOXX, down 3.8 percent after Goldman Sachs (GS) cut the stock to "neutral." Sodexo had already suffered a 15.7 percent decline after warning on profit in the previous session.
"We now see the pick-up of competitive pressures is unlikely to go away in the short term, while company profit continues to suffer from intensifying labor inflation in the region," GS analysts wrote.
Air France shares fell 3.2 percent after the airline said 75 percent of its flights would operate. The flag carrier's unions called a strike for wage increases amid a wider labor stoppage across France paralyzing rail services.
Acquisition news also continued to move the European market.
Eurofins Scientific shares fell 2.9 percent, the worst performers on the STOXX, after the firm acquired Lab Frontier in South Korea.
Italy's largest private broadcaster Mediaset nabbed the top spot on the FTSE MIB index, up 6.9 percent, after signing a content-sharing deal with Sky's Italian unit and paving the way for a broader alliance.
Liberum analysts called the deal a "win-win."
"This agreement should be a TV advertising revenue booster as it creates larger audiences," they wrote.
Berenberg upgraded Mediaset to a "buy," saying the deal marked a "step change in profitability."
Basic resources and oil and gas stocks were a rare bright spot, making gains as metals prices rose.
(Reporting by Helen Reid; Editing by Kit Rees and Mark Potter)