An extraordinary squeeze in the gold market has forced the main U.S. exchange to take action as the global pandemic shuts down physical trading routes just as investors are racing to buy the metal as a safe haven.

Banks and traders typically ship gold around the world on commercial flights, linking the trading hubs of London and New York with vaults and refineries in Switzerland, Hong Kong and Singapore. But as the coronavirus grounds flights and refineries shut down, it’s becoming harder to trade between global markets.

“This isn’t anything that we’ve seen in a generation because refiners never had to shutdown – not in war, not in the great financial crisis, not in natural disasters,” Tai Wong, the head of metals derivatives trading at BMO Capital Markets, said by phone Tuesday. “It’s never happened. And it happened astonishingly rapidly.”

At issue is whether there will be enough gold in New York to deliver against futures contracts traded on the Comex, which is owned by CME Group Inc. And it’s happening just as investors pile into gold—the quintessential safe haven asset at times of turmoil.

While the larger spot market in London is dominated by 400-ounce bars of gold, only 100-ounce and kilobars are deliverable on the Comex contract.

Gold futures on the Comex in New York shot to the highest premium to the London spot price in four decades on Tuesday. This morning, the difference was still nearly $40 an ounce. The skyrocketing spread between New York and London gold price underscores how desperate investors are to find a safe haven amid the market tumult brought on by the virus.

The last time the New York-London spread was this massive was in 1980—when the precious metals markets had been roiled by an oil shock and the Iranian revolution, as well as the Hunt brothers’ attempted corner of the silver market.

Late on Tuesday, CME said it would rush the launch of a new gold futures contract under which 400-ounce bars would also be deliverable. The move offers a way to address the squeeze, if holders of Comex futures are willing to exchange for the new contract.

“This new contract will provide customers with maximum flexibility in managing physical delivery,” said Derek Sammann, senior managing director and global head of commodity and options products at CME, citing “unprecedented market conditions.”

As of Tuesday, open interest in the April gold contract stood at 152,603 contracts, equivalent to 15.3 million ounces, but total deliverable stocks in Comex warehouses were just over half that.

Gold futures for June delivery climbed as much as 7.7% in New York on Tuesday and at their peak had a $67.57 an ounce premium over spot prices in London. Based on closing prices going back to the mid-1970s, the biggest spread between a most-active contract and spot gold was $67 in 1980, data compiled by Bloomberg show.

On Wednesday, most-active futures for June delivery were down 1.6% at $1,636.20 an ounce at 8:30 a.m. in London.

However, the pressure on the April contract continued, with April trading at an $8.40 premium to June—an indication of the level of the squeeze. On Tuesday, the April-June spread traded as high as $20 an ounce.

Ordinarily, banks and traders would ship supplies from refineries in Switzerland or Asia, which manufacture 100-ounce and kilobars for their investor clients, to New York in response to such a large Comex premium. But because of the outbreak, some have been reluctant to take advantage of the arbitrage out of fear that flights and truck deliveries will be canceled and trap their supplies, according to one senior trader, who asked not to be identified because the information isn’t public.

Peter Thomas, a senior vice president at Chicago-based broker Zaner Group, said that a similar dynamic was playing out in other precious metals markets such as silver.

“This hasn’t happened before, and this is very unique: We have a situation where there is silver available but no one will deliver it,” he said. “They won’t load the trucks. They won’t load the planes because the coronavirus. Even though there is product around they won’t pick it up.”