"Steel producers all over the world have greatly reduced steel production in response to a slowing global economy and the global outbreak of Covid-19, resulting in a significant drop in worldwide demand for coking coal," the CCTD said. "As a result, worldwide met coal producers have diverted most of their supply towards China at prices lower than domestic met coal producers."

The CCTD has called for authorities to strictly limit imported met coal volumes, and for steel producers who exceed set volume quotas to be banned from importing. Long-term contracts signed between mills and domestic met coal producers should also be strictly enforced and honoured.

Coking coal producers in China have complained that it has become increasingly difficult to maintain long-term contract relationships with customers with seaborne coking coal prices at low levels, while steel producers also have a duty to ensure that domestic met coal producers remain profitable.

Market participants see the complaint as a likely precursor to tighter import restrictions for Australian coal for the rest of this year, as many Chinese market participants have already suggested.

But the government could face an uphill task to reduce imports as import restrictions are already strict, some market participants said.

"How exactly tightened restrictions will be communicated to port authorities and the full extent of these restrictions still remain unknown," a Chinese trader said. "However, there are chances that all this could be executed by the first half of the year, given the current situation," the trader said.

"This came as domestic coal producers faced difficulties to executing their long-term contracts, but port restrictions at present are already quite tight so I wonder how much further they could go," a major China steel producer said. "Enforcement might be another major hurdle as importing of coal often involves various parties," the same producer added.

Four cfr China spot deals that lifted the premium low-volatile cfr index by $7.75/t today underscore this difficulty.

Customs authorities in Zhejiang province met with coal buyers to discuss the matter on 8 May. "The focus for Chinese customs this year is to ensure that steel producers still have access to imports when they need it, but clearance might be granted only on a case-by-case basis," an east China steel producer said. "Customs will also closely scrutinise imported coal and ensure that steel producers are not buying imports on behalf of traders, for instance."

China's government and industry associations such as CCTD have more often focused on thermal coal prices because power generation is an essential need for millions of people. This is the first time that the focus has instead been on coking coal, a steel-producing feedstock and so considered less essential. Coking coal accounts for around 15pc China's total coal production.

January-March coking coal imports rose by 80pc to 17.3mn t, the fastest start in at least six years, with the volume equal to about half the total year imports for 2015 and 2018. Seaborne supplies partly offset halted Mongolia imports.

April seaborne spot trades into China rose to a record high of 2.2mn t, up by 129pc from April 2019.

The assessment for premium hard low-volatile coking coal delivered on a cfr China basis has fallen by 33.9pc to $116.30/t from early March to last week. Sellers have rushed to dump unneeded coal cargoes into China as ex-China steel demand has collapsed during the Covid-19 outbreak.

China's domestic coking coal typically prices at a premium to seaborne. But the gap has widened with top-tier Chinese met coal at around a 30pc premium to the cfr China premium low-volatile index.