China on Wednesday warned it would take the "necessary measures" to protect its businesses after the United States launched a new trade probe into China's possible aluminium dumping.

The investigation into imports of aluminium sheet worth hundreds of millions of dollars a year was an unusually aggressive move by the United States.

For the first time since 1991, the US Commerce Department said it launched the investigation on its own initiative, rather than responding to a request from a US company.

"This practice by the US side is very rare in the history of international trade," China's Ministry of Commerce said in a statement.