The ability of policymakers in Beijing to roil global commodity markets has been underlined by a breathtaking rally in a key steelmaking ingredient that has caught consumers cold, but promises a profit windfall for the struggling mining industry.

The price of premium hard coking coal has more than doubled in the past six weeks to more than $200 a tonne as supplies have dwindled and buyers have scrambled to find cargoes in the spot market.

Behind the surge — or ‘met coal mania’ as it has been dubbed by one bank — are production curbs in China where the government is restricting the number of working days at domestic coal mines to 276 a year, down from 330.

This policy is mainly aimed at improving the profitability of its bloated and heavily indebted coal industry so it can repay loans to domestic banks. But it has also reduced output and tightened the global coking coal market. Its impact has been magnified by a string of disruptions in Australia, a leading supplier to the seaborne or export market.

If the price spike is sustained it could add billions of dollars to the bottom lines of the industry’s biggest producers, which include Anglo American, BHP Billiton, South 32 and Canada’s Teck. Coking coal is an important raw material used in blast furnace steel production.

“It’s been a perfect storm on the supply side,” said Christopher LaFemina, analyst at Jefferies.

Caught between an oversupplied Chinese market and faltering demand for steel, 2016 was supposed to bring more pain for the coking coal industry. But things have not worked out that way.

Instead of adding to last year’s 30 per cent drop, coking coal has staged a dramatic recovery, rising 164 per cent which has made it the best performing commodity of 2016.

“In bulk and base commodities if you get Chinese policy right you are a long way towards getting the market right,” said Colin Hamilton, head of commodities research at Macquarie.

China sprang its first surprise this year when policymakers, alarmed by slowing economic growth and capital flight, injected a huge amount of cash into the banking system. This boosted construction activity and demand for steelmaking materials such as iron ore and coking coal.

The credit surge was followed by the 276-day policy, which first lifted the price of thermal coal, used to generate electricity in power stations.

Coking coal did not start its vertiginous ascent until July when heavy rain and flooding reduced supply from Shanxi province. This forced Chinese buyers into the seaborne market, which was then hit by a number of unexpected outages at mines in Australia that further crimped supplies.

While about 300m tonnes of seaborne coking coal is produced each year most of it is traded on a contractual basis and priced off the spot market or monthly or quarterly averages. The amount of material readily available to buy — even when the market is not grappling with supply side issues, is very small — less than 10m tonnes according to Mr Hamilton.

“We have basically gone from $100 to $200 a tonne on the back of a few deals,” he said of the recent rally.

According to Ernie Thrasher, chief executive of US coking coal producer Xcoal, most of the recent buying in the spot market has come from steel mills in Europe and India. “They realised they needed coal but the market had started to run away from them,” he said. “Buyers tend to be much more reactive when the price goes against them.”

Industry watchers do not think the price surge can continue for much longer. Knowing that contract prices will rise in the fourth quarter — possibly to $170 a tonne — steel mills will have been buying as much as they can under existing arrangements. Many of these contract have options to buy an extra 10 per cent of agreed volumes, say traders.

Tom Price, analyst at Morgan Stanley said that road conditions in Shanxi had started to improve while China’s National Development and Reform Commission has requested a short-term lift in coal supply primarily to cap thermal coal prices.

Prices above $200 a tonne will also trigger a supply response, particularly from producers in North America.

Mr Thrasher said Xcoal would increase its exports and expected others to follow although they might take a bit longer — between three and six months. This is because many US mines were mothballed in 2015 while others were placed under Chapter 11 bankruptcy protection.

“What you will see at this price level is that anyone who can produce will produce,” he said.

However, few people expect prices to fall sharply unless Beijing performs a policy U-turn, something that seems unlikely in the near term.

“We expect supply increases to put some downward pressure on the coking coal prices in the very near future,” said Mr LaFemina. “But we do not expect a collapse to the levels of earlier this year as the government clearly wants to avoid financial stress in the domestic coal industry.”