The World Trade Organization on Wednesday handed a fresh victory to China, permitting it to slap duties on $645 million worth of US imports per year, in a long-running anti-dumping dispute with Washington.

The United States, which is unable to appeal against the decision, branded it  "deeply disappointing" and said it reinforced the need to reform the WTO's rules, saying they were being used to  "shield" China.

"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.

The WTO green light does not mean China will automatically impose the tariffs, in whole or in part, on US imports.

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 stretches all the way back to 2012, when the WTO set up a panel of experts to try to settle a complaint filed by China over what it said were unfair duties imposed by the United States.

Washington had justified the additional tariffs on products ranging from paper to tyres and solar panels, arguing they were being dumped on the market to help Chinese companies grab business.

The WTO Dispute Settlement Body ruled in China's favour and the ruling was upheld by its appeals judges in 2014, paving the way for China to retaliate.