The Chinese customs agency said Monday it will stop processing imports at midnight on September 5.
Wu visited Pyongyang in February past year, urging restraint after North Korea announced a plan to put a satellite into orbit with a long-range rocket.
China had pledged to fully enforce the sanctions after the USA accused it of not doing enough to rein in its ally which heavily depends on Beijing for its economic survival.
Chinese exports to North Korea rose nearly 30 per cent to $1.67 billion in the first half of the year, largely driven by textile materials and other traditional labour-intensive goods not included on the United Nations embargo list, Chinese customs spokesman Huang Songping told reporters.
Beijing issued the order on Monday.
The reason for the move, which was not publicly announced, was not clear, but it suggests Beijing was taking a tougher stance on trading with its northern neighbour even before the United Nations sanctions were announced. The suspension of coal imports deprives North Korea of massive income as it totalled United States dollars 1.2 billion a year ago.
China, a permanent member of the Council with the power of veto, voted in favour of Resolution 2371, which imposes sanctions against North Korea.
Imports were up an annual 60.3 per cent at 1.34 million tonnes worth an estimated US$68 million in the January-June period.More news: Kylie Jenner Bids Farewell To Her Teens W/ Mouthwatering Bikini Pics
"China and the US should continue to work together for the stable and sound development of China-US economic relations", said foreign ministry spokeswoman Hua Chunying.
Trump had planned to launch the trade investigation more than a week ago, but he delayed the move in favor of securing China's support for the new sanctions against North Korea, a senior administration official said late Friday.
"We will do our best to prevent (North Korea) from taking such acts by stepping up pressure through the UN", Prime Minister Shinzo Abe said on Monday. Xi, in his phone conversation with Trump, urged calm, the officials said.
South Korean President Moon Jae-In, a left-leaning leader who has previously advocated dialogue with the North, joined the appeals for restraint today.
Trump has also been critical of the North American Free Trade Agreement (NAFTA).In April, Trump said he had been ready to pull out, but he was talked out of it.
But its proposal for North Korea to suspend its arms programmes in return for the United States to halt military drills in the region has been ignored.
It is not known yet if the new envoy will visit North Korea any time soon but Hua said there will not be any change in Beijing's policy towards Pyongyang because of Kong's appointment.