* Global markets plunge, sterling hits 31-year low
* US investors brace for volatile stock trading session
By Noel Randewich
June 24 (Reuters) - S&P 500 and Nasdaq E-mini futures plummeted 5 percent early on Friday, hitting overnight limit thresholds, after Britain voted to leave the European Union, roiling global markets and raising fears of a shock to the world's economy.
The drastic drops in U.S. stock index futures prices suggest Wall Street will open with steep losses on Friday. Futures on the Dow Jones industrial average fell 4 percent.
British markets plunged, with sterling hitting a 31-year low in its biggest fall on record and UK stock futures pointing to a steep fall at the market open after Britons voted to leave the European Union. Asian markets also tumbled.
Sterling suffered its biggest fall on record as vote counts showed the Brexit camp had won the landmark referendum and investors grappled with its implications.
"It's going to be ugly in the morning. This is going to catch a lot of people wrong footed, end of discussion. Obviously markets were not pricing this in," said Mike Ellingsen, a stock trader at U.S. Global Investors Inc in San Antonio, Texas.
Reflecting fear among investors, futures on the VIX volatility index surged 10.57 points to 27.20.
The last time the CME had a circuit breaker triggered on index futures was August last year, when a major sell-off in Chinese stocks pummeled shares around the world.
On Thursday, U.S. stocks had risen as investors bet the United Kingdom would remain part of the European Union. (Additional reporting by Richard Leong and Rodrigo Campos; Editing by Cynthia Osterman, Leslie Adler and Kim Coghill)