President Trump said on Twitter the United States is considering halting trade with "any country doing business with North Korea."
His remarks came after North Korea detonated a nuclear device in its sixth and most powerful test on Sunday.
Geng Shuang, a Chinese Foreign Ministry spokesman, told reporters in Beijing on Monday that China regarded as "unacceptable a situation in which on the one hand we work to resolve this issue peacefully but on the other hand our own interests are subject to sanctions and jeopardised.
"This is neither objective nor fair."
China is the North's closest ally and commercial partner.
Asked whether Beijing would support tougher UN sanctions such as cutting off oil supplies to North Korea, Geng said whatever happened would depend on discussions among council members.
Geng said China, one of five permanent Security Council members with power to veto UN actions, would take part in a "responsible and constructive way."
He also expressed frustration at Australian Prime Minister Malcolm Turnbull's comment that Beijing had a responsibility to influence North Korea due to its status as the North's main trading partner.
"We keep stressing that we cannot solely rely on China to resolve this issue," Geng said. "We need all parties to work in the same direction."
A senior fellow at the Chongyang Institute for Financial Studies at the Renmin University of China, Liu Zhiqinm, told SBS News: “North Korea has its own desire, its own ambitions, in this region, and China has steadily tried to persuade North Korea to give up its nuclear test or nuclear ambition. But it refuses. So that violates Chinese wishes and Chinese dignity, I think. The people here are really losing patience with North Korea.
“[Kim Jong-un is], really, a naughty boy. Nobody can control him. This is the point. But one thing we can see [is] that China can help from one side, and [from] the other side America should coordinate with China. America is the key element to find a solution in this issue.
“I think, with time passing, that North Korea will be feeling more pressure from China.”
