President Donald Trump's harsh new sanctions for North Korea rile China

President Donald Trump has warned of a "phase two" that could be "very, very unfortunate for the world" if the sanctions against North Korea did not work. Photo / AP

China has reacted with anger to new US sanctions aimed at increasing pressure on nuclear-equipped North Korea, saying the unilateral targeting of Chinese firms and people risked harming co-operation on the problem.

The US said on Friday it was imposing its largest package of sanctions aimed at getting North Korea to give up its nuclear and missile programs, and President Donald Trump warned of a "phase two" that could be "very, very unfortunate for the world" if the steps did not work.

In addressing the Trump administration's biggest national security challenge, the US Treasury sanctioned one person, 27 companies and 28 ships, according to a statement on the US Treasury Department's website.

The sanctions' targets include a Taiwan passport holder, as well as shipping and energy firms in mainland China, Hong Kong, Taiwan and Singapore. The actions block assets held by the firms and individuals in the US and prohibit US citizens from dealing with them.

In a terse statement, China's foreign ministry said the government had always fully and thoroughly enforced United Nations resolutions on North Korea, and absolutely did not allow any of its citizens or companies to contravene them.

China will "seriously handle" in accordance with the law those found to have done so, it added.

"China resolutely opposes the US side enacting unilateral sanctions and 'long- armed jurisdiction' in accordance with its domestic law against Chinese entities or individuals," the ministry said.

"We have already lodged stern representations with the US side about this issue, and demand the US side immediately stops such relevant mistaken actions to avoid harming bilateral cooperation in the relevant area," it added, without elaborating.