Insurance firms have started covering charter flights to carry gold, helping to ease logjams in the bullion supply chain that caused prices to diverge sharply in different markets, the London Bullion Market Association (LBMA) said on Thursday.

Gold is usually moved between countries in the holds of passenger planes, but most flights around the world have been grounded by measures to control the spread of the coronavirus.

Worries that it may be impossible to ship gold quickly from London, a major storage center, to New York have pushed U.S. gold futures prices far above London spot levels.

Dealers in bars and coins have also faced shortages, with demand for gold, traditionally seen as a safe haven asset, accelerating as the economic impact of the virus become clearer.

“Charter flights have now been approved by insurers in terms of shipping gold,” LBMA CEO Ruth Crowell told a conference call with market participants, calling it a “positive and significant development.”

Charter flights remained expensive, however, because of increased competition, she said.

Adding to supply disruption are the partial or full closure of some precious metals refineries, a particular problem because countries often want gold of different shapes and sizes, meaning metal must be melted and recast before delivery.

Three plants in Switzerland, the most important refining center, partly reopened this week.

Crowell said refiners in China had reopened and three of the world’s biggest in other countries – Rand Refinery in South Africa, Australia’s Perth Mint and the Royal Canadian Mint – had been recognized by governments as essential businesses.

“There’s definitely enough refining capacity. The challenge … is still one of logistics,” she said.

Crowell also said operators of precious metals vaults had agreed to cooperate to increase capacity on a best effort basis if one of the vaults closes, but this mechanism had not been triggered as vaults remained open.