All three major indexes are having worst week since 2011

This could spell more trouble
VIX doing something extraordinary
Hardest hit Dow stocks

Following a steep market decline on Thursday, all three major indexes spluttered through the trading session on Friday, leading to one of the worst weeks since 2011. (Tweet this)

Less than an hour before the closing bell, the Dow briefly entered correction territory on an intraday basis when it neared 6,516.22. To be in correction from its closing high of 18,312.39, the Dow has to hit 16,481.15. The Nasdaq also came very close to correction territory.

This week marked the worst for the since the week of Sept. 23, 2011 when it lost 6.54 percent. The Dow Jones industrial average is also having its worst week since then, when it had dipped 6.4 percent. The Nasdaq is having its worst week since August of 2011.

The Dow has fallen more than 500 points three times in the past five years. The last time was on Aug. 10, 2011 when the Dow dropped 519.83 points.

The Dow ended Friday's session down 528.47 points at 16,462.22. The S&P ended at 1,971.29, down 64.44 points. The Nasdaq closed down 171.45 points at 4,706.04.

Traders work on the floor of the New York Stock Exchange.
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Stocks extended their plunge on Friday as concerns about slowing global growth continued to weigh on investors.

Here are some other milestones hit this week:

  • If the S&P 500 surpasses a dip of 4.69 percent, it will be the worst week since Sept. 2011
  • If the Dow falls below the 4.78 percent level, it will also be the worst week since Sept. 2011
  • The Nasdaq is looking at its third worst week over the past five years
  • If the Nasdaq finishes down more than 6.62 percent, it will be the second worst week over that period
  • The VIX posted its largest monthly gain through 1990 and is up over 100.4 percent month-to-date in Aug. (that is bigger than the 90.75 percent gain of Sept. 2008 and the Aug. 1998 gain of 78.55 percent)
  • Friday's cumulative volume was 10.28 billion shares traded (compared to 5.2 billion shares traded last Friday)
  • Friday was the biggest volume day of the year, dating back to Dec. 19, 2014
  • Almost 1 billion shares were traded as of 3 p.m. ET
  • The Nasdaq has to hit 4,708.75 to be in correction mode from its all-time intraday high of 5,231.94 from July 20
  • The S&P 500 has to hit 1,921.25 to be in correction mode from its intraday all-time high of 2,134.72 from May 20
  • The Dow closed in correction off 10.3 percent from its May19 all-time intraday high (the biggest point drop for the Dow since Aug. 8, 2011)
  • The Nasdaq closed in correction off more than 10 percent from its July 20, 2015 all-time intraday high
  • Apple closed down over 21 percent from its April 28 52-week high
  • The Russell 2000 closed in correction off 10.54 percent from its June 23 52-week high
  • The Dow is down 1,017 points this week and 1,230 points this month

—CNBC's Gina Francolla, Christopher Hayes and Evelyn Cheng contributed to this report.