China says it will stop importing North Korean coal, iron ore, fish and other goods in September as it implements United Nations sanctions.
The UN Security Council, including China, backed a new resolution last weekend imposing fresh sanctions on the rogue state in retaliation for its controversial nuclear programme.
The sanctions aim to block US$1bn worth of North Korean exports - about a third of its total exports.
The Chinese government said the imports will stop on September 5th.
It came as US Joint Chiefs of Staff Chairman Joseph Dunford said military options were being prepared against the North if diplomatic and economic sanctions failed.
The office of South Korean President Moon Jae-in said Mr Dunford made the comments in a 50-minute meeting to discuss North Korean provocation.
Last week, US President Donald Trump said he was ready to unleash "fire and fury" if North Korea continued to threaten the United States.
Tensions have increased over fears North Korea is close to achieving its goal of putting mainland US within range of a nuclear weapon.
North Korea has threatened to fire intermediate missiles into waters off the coast of the US overseas territory of Guam.
North Korean leader Kim Jong Un and US President Donald Trump
It plans to time its launch to coincide with annual drills involving US and South Korean forces, taking place later this month.
The North's state news agency said about 3.5 million of its students and workers have volunteered to fight alongside the military to defend their country from the US.
China, meanwhile, has appointed a new special envoy for the North Korean issue.
China is North Korea's closest ally, but it has been angered by its repeated missile and nuclear tests.
President Xi has urged Washington and Pyongyang to avoid words or actions that could worsen the situation.
The South Korean president called for a peaceful solution, saying that there must not be another war on the Korean Peninsula.
President Trump has called for China to do more to stop the North's nuclear ambitions.