* Disney, Viacom lead media selloff
* S&P media index records worst two-day tumble since 2008
* Tesla, Green Mountain fall after results
* Indexes down: Dow 0.7 pct, S&P 0.75 pct, Nasdaq 1.53 pct (Updates to mid-afternoon)
By Noel Randewich
Aug 6 (Reuters) - Wall Street slumped on Thursday as weak earnings reports from media companies raised fears that more viewers are ditching cable TV, dragging the sector to its worst two-day loss since the financial crisis.
The selloff was compounded by nervousness ahead of key jobs data on Friday that could provide clues about the timing of the first Federal Reserve interest rate hike in almost a decade.
Viacom fell as much as 23.6 percent to its lowest in almost four years after reporting lower-than-expected quarterly revenue due to weakness in its cable TV business. Walt Disney was off 2.9 percent and down for a second session after it lowered profit guidance for its cable networks unit on Tuesday.
The S&P 500 media index was down 2.85 percent, recording it's biggest two-day fall since November 2008, with Time Warner, Comcast and CBS all in the red and Twenty-First Century Fox down 6.6 percent.
"All the media stocks are down and it seems people just want to get out of the sector at any cost and take any loss," CLSA analyst Vasily Karasyov said. "The selling pressure is relentless."
Viacom's results and Disney's warning put the spotlight on a trend of viewers shifting from cable TV to Internet-based services such as Netflix, which was up 1 percent.
At 2:36 pm the Dow Jones industrial average or 0.7 percent at 17,418.11. The S&P 500 lost 0.75 percent to 2,084.19 and the Nasdaq Composite was down 1.53 percent at 5,061.48.
Eight of the 10 major S&P sectors were lower, with the health index's 1.84 percent fall leading the decliners.
In other earnings-driven stock moves, Tesla fell 8.91 percent and Keurig Green Mountain slumped as much as 30 percent after reporting disappointing numbers.
Investors were also jittery ahead of the release of U.S. non-farm payroll numbers, which are expected to have risen by 223,000 in July, matching gains in June.
The Fed has said it will raise rates only when it sees a sustained recovery in the economy.
In more earnings action, Marathon Oil, Monster Beverage and Zynga were due to report after market close.
Declining issues outnumbered advancing ones on the NYSE at a rate of 1.61 to 1. On the Nasdaq, that ratio was 2.39 to 1 favoring decliners.
The S&P 500 index was posting 17 new 52-week highs and 44 new lows; the Nasdaq Composite was recording 59 new highs and 159 new lows. (Additional reporting by Tanya Agrawal and Lehar Maan, Editing by Saumyadeb Chakrabarty and Meredith Mazzilli)