U.S. equity futures plunged deeper into the red Tuesday, setting up investors for the biggest two-day decline since August as investors continued to retreat from record highs in global stocks amid concerns over valuations in the tech sector and a worrying rise in government bond yields.

The Dow Jones Industrial Average is looking at its second consecutive triple-digit decline, according to futures prices, with contracts tied to the benchmark priced 243 points lower from Monday's closing levels. S&P 500 futures also slumped in early European trading and were marked 13.5 points, or 0.47%, to the downside after the largest single-day loss for U.S. stocks in at least five months yesterday on Wall Street.

The Dow's losses were multiplied by sharp declines for stocks in the pharma sector after Amazon Inc. (AMZN) - Get Report , Berkshire Hathaway Inc. (BRK.A) - Get Report and JPMorgan Chase & Co. (JPM) - Get Report said they would create a non-profit healthcare company for its U.S. employees.  UnitedHealth Group Inc.  (UNH) - Get Report , a Dow component, was marked 6.63% lower in pre-market trading, indicating an opening bell price of $231 each while CVS Health Corp (CVS) - Get Report was seen 5.2% lwoer at $79.29. 

Apple Inc. (AAPL) - Get Report shares was another notable premarket mover, extended declines Tuesday following its biggest single-day drop in more than a month as investors continue to question the strength of demand for its flagship iPhone X ahead of its first quarter earnings release later this week.

Apple shed $14 billion in market value Monday amid a 2.07% slump that was driven, in part, by a report from Japan's Nikkei Business newspaper which suggested the world's biggest tech company was ready to halve its forecasts for iPhone X shipments to 20 million for the three month period that beings in January, the company's fiscal second quarter.

Apple shares were marked 1.33% lower in premarket trading Tuesday, indicating an opening bell price of $165.73 each, a move that would push the stock to its lowest level since Nov. 1 and tip it into negative territory since the $999 iPhone X was launched on Nov. 3.

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Consumer confidence data for the month of January will be published by the Conference Board at 10 a.m. ET while fourth-quarter earnings in a busy week of corporate reports are expected from McDonald's Corp. (MCD) - Get Report , Pfizer Inc.,  (PFE) - Get Report , Advanced Micro Devices Inc. (AMD) - Get Report , Corning Inc. (GLW) - Get Report and Harley-Davidson Inc. (HOG) - Get Report

In Europe, the Stoxx 600 index fell 0.56% by mid-morning trading to 397.58 points, the lowest since Jan. 25, as benchmarks around the region booked declines of between 0.15% and 0.3%. In Britain, a weaker pound failed to support stocks as the FTSE 100 slumped 0.7% amid reports that data compiled by the government as part of its Brexit analysis shows the economy would lose 5% of its value over the next 15 years even under the best-case scenario the U.K. could arrange as it leaves the European Union.

Overnight in Asia, stocks were also noticeably lower following Wall Street's sharp decline, with the MSCI Asia ex-Japan index falling 1.28% to 605.80 points and the Nikkei 225 benchmark in Tokyo retreating 0.7% to close at 23,455.98 points, even as the yen weakened against a modestly rebounding U.S. dollar, wiping out all of its gains for the month of January. 

The dollar index, which benchmarks the greenback against a basket of six global currencies, gained 0.1% in early trading to change hands at 89.32 as investors pulled the buck from three-year lows amid yesterday's sharp rise in U.S. Treasury yields, but reversed that move to 89.11 after a solid reading on Eurozone economic growth, where GDP expanded 2.6% last year, which helped boost the euro -- the biggest influence in the dollar index basket -- 0.27% higher to 1.2414. 

Benchmark 10-year notes were marked at 2.69% in European dealing after hitting an April 2014 high of 2.72% yesterday as investors fretted about faster inflation amid the resurgent global economy.

Global oil prices also extended declines in Tuesday trading as investors booked profits from crude's long six-week rally ahead of data on domestic U.S. crude stocks later today from the American Petroleum Institute. 

Brent crude futures for March delivery, the global benchmark, were seen 0.67% lower from their Monday close at $68.99 while WTI contracts for the same month fell 0.7% to 65.08 per barrel. 

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