Rohingya Muslims in Myanmar are facing a catastrophic humanitarian situation, according to the UN secretary general.
China has endorsed Myanmar's offensive against Rohingya Muslim insurgents, though the UN secretary-general says the operation, which has forced nearly 400,000 people to flee to Bangladesh, is best described as "ethnic cleansing".
The Myanmar military offensive in the western state of Rakhine was triggered by a series of guerrilla attacks on August 25 on security posts and an army camp in which about a dozen people were killed.
"The stance of China regarding the terrorist attacks in Rakhine is clear, it is just an internal affair," the state-run Global New Light of Myanmar newspaper quoted China's ambassador, Hong Liang, telling top government officials.
"The counter-attacks of Myanmar security forces against extremist terrorists and the government's undertakings to provide assistance to the people are strongly welcomed."
China competes with the United States for influence in Myanmar, which in 2011 began emerging from nearly 50 years of strict military rule and diplomatic and economic isolation.
Earlier this week, the Trump administration called for protection of civilians.
The violence in Rakhine State and the exodus of refugees is the most pressing problem Nobel Peace laureate Aung San Suu Kyi has faced since becoming national leader last year.
Suu Kyi will miss the UN General Assembly's ministerial session, which starts on September 19 and runs to September 25 to address domestic security issues.
Critics have called for her to be stripped of her Nobel prize for failing to do more to halt the strife which the UN rights agency said was a "textbook example of ethnic cleansing".
UN Secretary-General Antonio Guterres and the UN Security Council on Wednesday urged Myanmar authorities to end violence, adding that the situation was best described as ethnic cleansing.
"When one-third of the Rohingya population had to flee the country, could you find a better word to describe it?" he told a news conference in New York.
The government says it is targeting "terrorists," while refugees say the offensive aims to push Rohingya out of Buddhist-majority Myanmar.
Numerous Rohingya villages in the north of Rakhine state have been torched but authorities have denied that security forces or Buddhist civilians have been setting the fires. Instead, they blame the insurgents.
But international pressure is growing on Myanmar.
The 15-member Security Council met behind closed doors on Wednesday, at the request of Sweden and Britain, to discuss the crisis for the second time since it began and agreed to publicly condemn the situation.
The council "expressed concern about reports of excessive violence during the security operations and called for immediate steps to end the violence in Rakhine, de-escalate the situation, re-establish law and order, ensure the protection of civilians ... and resolve the refugee problem".
British UN Ambassador Matthew Rycroft said it was the first statement from the Security Council on Myanmar in nine years. Such statements have to be agreed by consensus and Russia and China have traditionally protected Myanmar from any action.
Bangladesh says all the refugees will have to go home and has called for safe zones in Myanmar.
Aid agencies will have to step up operations "massively" in response to the refugee flow to Bangladesh, a senior UN official said, adding the $US77 million ($A96 million) the United Nations had appealed for last week would not be enough to deal with the crisis.