Sharp declines in U.S. stock index futures triggered trading curbs meant to slow panicked markets as the price of oil fell by more than 30 percent and bond yields crashed amid heightened worries over the coronavirus.

E-mini futures on the S&P 500 dropped by 5 percent in overnight trading Sunday, triggering automatic trading curbs that kick-in when the price falls below 5 percent of the closing price of the referenced index Friday. As a result, the futures contract cannot trade at a lower price until the cash market opens at 9:30 a.m., although trades may still be made at higher prices.

The last time futures trading hit the overnight limit was election night of 2016, when markets initially sold off following the news that Donald Trump had won the election. That selling pressure quickly subsided and the major indexes closed up by around 1 percent or so the following day.

The E-mini is an electronically traded futures contract based on the underlying S&P 500 index. The contracts are around one-fifth the size of the standard S&P futures contracts, earning them the monicker “mini.” They are considered highly liquid and are widely traded but they have, in a few past episodes, been prone to so-called “flash crashes.”

By early Monday morning, futures on the Nasdaq Composite and Dow Jones Industrial Average had also tripped trading curbs.

The chaotic market action was not confined to equities futures on Sunday. Investors bid up Treasuries, pushing yields down to new record lows, and oil prices tanked.

The yield on the 10-year Treasury note sank as low as 0.32 percent in overnight trading Sunday before bouncing back to slightly over 0.5 percent. The yield on 30-year Treasuries fell below 1 percent for the first time ever and touched as low as 0.70 percent.

Oil prices crashed more than 30 percent Sunday night after Saudia Arabia on Saturday slashed official crude prices for April following the collapse of talks between OPEC+, which includes the traditional OPEC nations plus Russia. Oil had fallen sharply on Friday following the news that talks had fallen apart but took an even deeper tumble, falling an additional 20 percent or so, when it became apparent that the once allied oil producers were now engaged in a price war to take market share from each other.

Low oil prices were an unambiguous boon to the U.S. economy, boosting consumer buying power and keeping a lid on inflation. But now that the U.S. is once again a major world oil producer, low oil prices can weigh on employment, manufacturing, and the financial stability of heavily-leveraged U.S. drillers. That could even shake some regional banks with large exposures to the drillers.