Beijing on Saturday accused the United States of "bullying" after Washington announced export controls on dozens of Chinese firms over alleged ties to China's military.

The announcement -- in the final weeks of President Donald Trump's term -- comes after relations between Washington and Beijing soured under his administration, which saw the US start a trade war with China and expand its list of sanctioned entities to a few hundred Chinese companies and subsidiaries.

China's commerce ministry on Saturday said it "firmly opposes" the move, which will affect the country's biggest chipmaker, SMIC, and vowed to "take necessary measures" to safeguard Chinese companies' rights.

The ministry accused the United States of "abusing export controls and other measures to continuously suppress" foreign entities, and urged Washington to "stop unilateralism and bullying".

US Commerce Secretary Wilbur Ross on Friday said the designations, which restrict US companies' abilities to do business with the firms, are over an array of charges including human rights abuses and the activities of the Chinese military -- particularly in the South China Sea -- as well as theft of US technology.

SMIC has received billions of dollars in support from Beijing and is at the heart of its efforts to improve the country's technological self-sufficiency.

The designation means US companies must apply for a licence before exporting to SMIC, and specifically targets the Chinese firm's ability to acquire materials for producing chips of 10 nanometres or smaller, the best class in the industry.