A trade surplus was posted by China of more than $42.76 billion during June, slightly higher than forecasts by analyst for a $42.43 billion surplus and wider than the previous month of $40.80 billion.
U.S. president Donald Trump has criticized China's ties with the North Korean government, saying its economic interests undermined its ability to challenge president Kim Jong-un's totalitarian rule.
The decline follows China's decision in February to ban all imports of North Korean coal.
But Huang added that imports from North Korea had sharply decreased every month since March and insisted that Beijing was upholding United Nations sanctions against Pyongyang over its nuclear programme.
While Beijing is North Korea's longtime ally in the region, the state has voiced frustration with North Korean leader Kim Jong Un's aggressive behavior.
China's exports to North Korea rose 29.1 percent in the first half of 2017, driven by consumer goods such as textiles that aren't on the sanctions list, Huang said.
Imports fell 13.2 percent to $880 million in the six months to June 30 from the same period a year earlier, the customs bureau said Thursday.
The growth bilateral trade "should not be used as basis for questioning China's solemn attitude towards the implementation of the Security Council's resolutions", Huang Songping, a spokesman for Chinese Customs, told reporters in Beijing.
At the same time, Cui stressed that U.N. Security Council sanctions on North Korea did not constitute an embargo.
Tensions rose after North Korea's test this month of an intercontinental ballistic missile that could reach the United States mainland.
That is thanks in a large part to the resilient demand for real estate in smaller cities across China with lax rules for properties as authorities attempt to clear up the housing glut.
The overall rise in trade has been driven by China's exports to North Korea, which were up by almost 30% in the first half of the year. "But we are skeptical that the current pace of imports can be sustained for much longer given the increasing headwinds to China's economy from policy tightening".
Though Trump took a more conciliatory tone on the North Korea issue and China's role at a meeting with Chinese President Xi Jinping.