China said Tuesday it opposes a US decision to bring criminal charges against a Chinese firm and executives for their alleged role in supporting North Korea's nuclear weapons programme.

"We would like to stress we oppose any country carrying out so-called 'long-arm jurisdiction' over a Chinese entity or individual in accordance with its own domestic laws," said foreign ministry spokesman Geng Shuang.

Beijing has expressed its position directly to the US in recent communications, he added during a regular briefing.

On Monday the US Justice Department announced criminal charges against the Dandong Hongxiang Industrial Development company and four Chinese nationals for conspiring to evade US sanctions on North Korea, violating US regulations against support for "weapons of mass destruction proliferators", and money-laundering.

In parallel the Treasury added the company and the four individuals to a sanctions blacklist, making them ineligible to do business with American individuals or companies, particularly financial firms.

The move follows an earlier announcement by Chinese authorities that they were investigating the company, located in the city of Dandong on the border with North Korea.

Geng said Beijing would "seriously punish any illegal activities by companies or individuals, once discovered".

He added that China was willing to cooperate with other countries, if needed, on the basis of "mutual respect and equal treatment." He also stressed that China opposes Pyongyang's nuclear programme and has been "faithfully observing" its commitment to UN sanctions.

However, customs data released Monday showed China's imports of North Korean coal have surged 60 percent since the latest sanctions went into effect in April, reaching nearly 2.5 million tonnes valued at $113 million.

Dandong Hongxiang logged more than $530 million in two-way trade with North Korea between 2011 and 2015, according to a recent report by the Asan Institute for Policy Studies in Seoul and C4ADS in Washington.

That could have been enough to fund North Korea's uranium enrichment facilities, and to design, make, and test its nuclear weapons, the report said.

The North carried out its fifth and most powerful atomic weapons test this month, sparking moves to impose even tougher sanctions.