Russia’s options in fighting back also face western sanctions.

Moscow has built up foreign exchange reserves to more than $630bn, from $356bn in 2015, but Berenberg Bank estimates almost two-thirds are effectively frozen by international restrictions.

Meanwhile, forcing companies to sell their foreign exchange can offer only temporary support, and undermine their ability to buy imports. Banning foreigners from selling assets prevents a short-term outflow, but will also scare them from coming back in future.

Sanctions allow for energy purchases, giving Russia a vital source of hard currency – but potentially making it harder for the Kremlin to threaten to close the gas pipelines in retaliation, for fear of losing its remaining financial lifeline.

As it stands China has not signed up to western sanctions, so will become an increasingly important supplier to, and customer of, Russian industry.

“Regarding financial sanctions, we do not support that,” said Guo Shuqing, head of China’s banking regulator. He added that “unilateral” sanctions did not effectively address problems.

Beijing’s decision tears a hole in sanctions. Mark Williams at Capital Economics says there are limits even to China’s ability to help, however, as its companies will not want to do business with Russia, particularly if it means risking their ability to sell to nations such as the US.

Henry Wilkinson of security intelligence firm Dragonfly says dealings with Russia risks a “reputational risk” for businesses “on a scale I’ve not seen before.”

Ultimately, he says, cutting it off from global goods and services could become a serious political risk in the country if “mass unrest” follows: “We shouldn’t just idly assume Putin is completely safe.”

But the former central banker holds out little hope for a result that would spur cheer in the west: “The Russian financial sector is in danger – but even if it fails it would lead to nationalisation and a non-market financial model instead of leading to Putin returning his troops from Ukraine.”