Japan has decided to join in a US complaint against China at the World Trade Organisation over Beijing's industrial subsidies, a report said Friday.

In the complaint, Japan will explain how Japanese firms have also been damaged by the subsidies, the Nikkei newspaper said, citing unnamed sources.

The United States took China to the WTO on February 2, getting tough after years of quiet diplomacy. The global body will set up a settlement panel if the two nations fail to iron out the dispute within 60 days.

When bringing the case to the WTO, the United States said it invited its foreign partners including the European Union and Japan to join the case.

China is Japan's largest trade partner, with Japanese companies depending on their giant neighbour as an industrial base and increasingly as a market for consumer goods.

The United States alleges that Beijing's state subsidies for steel, paper, information technology and other industries make Chinese goods artificially cheap and prevents US companies from competing fairly.

The United States hauled China to the world body just after the Democrats, who have traditionally been more critical of China on trade issues, took control of the US Congress.