Update: Trading resumes in New York after S&P 500 plunge

If the decline hits 20%, markets will close for the day.

US stocks plunged the most since the 2010 flash crash as a full-blown crude price war rattled financial markets already on edge over the spreading coronavirus. Treasury yields plummeted, oil sank more than 30% and credit markets buckled.

The S&P 500 is now down almost 19% from its Feb. 19 all-time high, threatening to end the record-long bull market that began 11 years ago to the day. NYSE circuit breakers halted trading for 15 minutes starting at 9:34 am in New York, in a move designed to limit panic. The next circuit breaker will trip if losses reach 13%.

If the decline hits 20%, or 2,377.9, markets will close for the day. Only the 20% rule applies in the final 35 minutes of cash trading. Traders have never seen a 13% or 20% breaker trip.

“Even though people are concerned it could create more problems, it does allow people to step back and re-assess what they’re doing,” said Matt Maley, an equity strategist at Miller Tabak & Co. “The one thing is, it’s been a long time since any of these circuit breakers kicked in. Back then, it was positive. It allowed people to calm down a little bit.”

The last time the futures trading limits hit was Nov. 8, 2016, following Donald Trump’s shock election victory. This time, a plunge in oil prices added to weeks of concern that the spreading coronavirus will derail the the global economy. Crude oil fell as much as 34% to $27.34 a barrel, the worst day since the Gulf War in 1991, after Saudi Arabia initiated an all-out price war.

Volatility has reigned in markets around the world amid an outbreak that has infected more than 108,000 people. At least 10 billion shares have traded on U.S. exchanges each day for two weeks, and the VIX has closed above 30 for seven days straight. Such turbulence is putting the vitality of the longest-ever bull market in jeopardy.