China has said Donald Trump's threat to cut off trade with countries that deal with North Korea is unacceptable.
Mr Trump warned that the US was considering halting trade with "any country doing business with North Korea" in response to the North's latest nuclear test and hydrogen-bomb claim.
In response to Mr Trump's threat, Chinese foreign ministry spokesman Geng Shuang said it was not fair - as China had worked on resolving the North Korea issue via talks and that effort was not being recognised.
:: US options to deal with N Korea squeezed by new threats of violence
"What we absolutely cannot accept is that on the one hand (we are) making arduous efforts to peacefully resolve the North Korean nuclear issue, and on the other hand (our) interests are being sanctioned or harmed," he said.
"This is both not objective and not fair."
China, which said it has lodged an "solemn" complaint with Pyongyang and continues to support "denuclearisation", is North Korea's closest ally and biggest trading partner.
:: Who is North Korea's 'nuclear' newsreader?
It also urged North Korea not to launch any further missiles, as US Security Council resolutions prohibit it.
America's defence secretary earlier warned North Korea that any threat to the US and its allies would be met by a "massive military response".
Speaking outside the White House, James Mattis said America's response would be "both effective and overwhelming" if it was put in danger.
"We are not looking to the total annihilation of a country, namely North Korea. But we have many options to do so," he said.
:: Key steps in North Korea's nuclear and ballistic missile ambitions
Leaders of the BRICS grouping of emerging economies - Brazil, Russia, India and China - said in a joint statement they "strongly deplore" North Korea's latest nuclear test at their annual summit.
Russian deputy foreign minister Sergei Ryabkov warned that "any clumsy step" could lead to an "explosion" and called for a diplomatic solution and "those who are stronger to show restraint".
Egypt, Australia and Germany also expressed concerns and Switzerland said it would be prepared to host talks.
Despite tough talk from the US, the immediate response from the international community is likely to focus on enforcing even tougher economic sanctions on the isolated state.
:: North Korea's nuclear test was diplomatic weapon to divide US and China
The UN Security Council has scheduled an emergency meeting at the request of the UK, Japan, France, South Korea and the US - its second urgent session in less than a week.
Downing Street restated the UK's "overwhelming" preference for a peaceful and diplomatic resolution to the crisis.
According to diplomats, the Security Council could consider banning North Korea's national airline and textile exports from Pyongyang, as well as halting the supply of oil to its government and military.
North Korean nationals could also be prevented from working abroad, and its top officials could be subjected to an asset freeze.
Such economic penalties have had little effect on Pyongyang's nuclear ambitions in the past.