SAN FRANCISCO (Reuters) - So-called FANG stocks and other tech shares sank in extended trade on Thursday following disappointing quarterly reports from Amazon.com Inc AMZN.O and Alphabet Inc GOOGL.O.

The weak results from Amazon and Google parent Alphabet were the latest setback for the high-growth quartet of stocks known as FANG, which also includes Facebook Inc FB.O and Netflix Inc NFLX.O.

Nasdaq futures NQcv1 fell 0.8 percent and S&P futures EScv1 lost 0.5 percent, suggesting the U.S. stock market may see more selling when it opens on Friday.

Wall Street favorites in recent years, the FANG stocks have been punished in a month of volatility for U.S. equities that has some investors worried a decade-old bull market may be ending.

The FANG group, along with heavyweight tech stocks Apple and Microsoft MSFT.O, have made outsized contributions to the S&P 500's gains in recent years, and a prolonged downturn for those stocks would be a major setback for the market.

After the bell, Amazon tanked 8 percent. The fall came after the online retailer and cloud computing heavyweight reported that its quarterly net sales rose to $56.58 billion from $43.74 billion a year earlier. That missed analyst estimates of $57.1 billion, according to Refinitiv data.

Alphabet missed analysts’ estimates for third-quarter revenue, while rising expenses trimmed its operating margin for the third straight quarter, fanning concerns about regulatory scrutiny. Its stock fell 4.7 percent.

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Reacting after hours, Netflix dipped 3 percent and Facebook, which reports results on Oct. 30, lost 2.3 percent.

During Thursday's official trading session, all four FANG stocks rallied by between 3 percent and 7 percent, regaining some of the territory lost in recent weeks during a broad market sell-off. The Nasdaq .IXIC jumped 2.95 percent, but remained down 10 percent from its August record high close.

Apple AAPL.O fell 1.6 percent after hours, while Twitter TWTR.N dipped 2.5 percent. Earlier in the day, Twitter surged 15 percent in its biggest one-day gain in a year after the social media company easily beat Wall Street's revenue and profit estimates.

Snap SNAP.N slumped 11 percent in extended trade after the Snapchat owner said its number of daily active users fell to 186 million in the third quarter from 188 million in the June quarter, hurt largely by an app redesign and competition from Facebook's Instagram.

Chipmaker Micron Technology MU.O lost 3.8 percent in extended trade after Western Digital WDC.O said it was taking steps to align its output of flash memory chips with projected weak demand. Western Digital dropped 8 percent in extended trade.

Intel Corp INTC.O jumped 3.5 percent in extended trade after posting one of Thursday's few upbeat quarterly reports.