The World Trade Organisation has permitted China to retaliate with duties on $645m worth of US imports per year, in a long-running anti-dumping dispute between Beijing and Washington.

"In light of the parties' arguments and evidence in these proceedings, we have determined that the appropriate level... is $645.12 million per annum," a WTO arbitrator ruled.

Therefore, "China may request authorisation from the DSB (Dispute Settlement Body) to suspend concessions or other obligations at a level not exceeding $645.121 million per annum".

The figure was revealed in an 87-page decision by a WTO arbitrator on the level of countermeasures Beijing could request in its dispute with Washington regarding US countervailing duties (CVD) on certain Chinese products.

The dispute over subsidy duties stretches all the way back to 2012, when China filed a request for consultations with the United States.

Beijing was challenging US measures relating to the imposition of CVD on a range of Chinese goods.

The US government has said the decision was "deeply disappointing" and underscored the need for WTO reforms.

Adam Hodge, spokesperson for the US Trade Representative's office said the decision by the WTO arbitrator "reflects erroneous Appellate Body interpretations that damage the ability of WTO Members to defend our workers and businesses from China's trade-distorting subsidies."

He said the decision "reinforces the need to reform WTO rules and dispute settlement, which have been used to shield China’s non-market economic practices and undermine fair, market-oriented competition."