The Trump administration has once again declined to brand China a currency manipulator, but it did target that country and five others for special monitoring for what the administration says are practices that are worsening America's trade deficit.

In a report it must issue every six months, the administration said on Friday that no country met the criteria to be labelled a currency manipulator. But six nations - China, Japan, South Korea, India, Germany and Switzerland - were placed on a watch list subjecting them to added US pressure to lower trade surpluses.

No country has been labelled a currency manipulator by the United States since the Clinton administration tagged China in 1994. Credit:AP

India is new to the list. The five other nations had been cited in October. The report comes at a time President Donald Trump is threatening to impose penalty tariffs on China and other nations.

Those threats have sent global financial markets on a roller-coaster ride, with stocks plunging when the threat of a tit-for-tat trade war looked imminent and then rebounding when both sides cooled the tough talk. Trump first threatened tariffs on $US50 billion of Chinese goods and then asked his top trade negotiator to find another $US100 billion in Chinese products to target.