The US and EU issued an impassioned plea on Thursday for greater international efforts to tackle an emerging famine in Ethiopia's Tigray and end the conflict wracking the region.

"Famine may already be happening in certain areas, threatening the lives of hundreds of thousands. It's unconscionable," US ambassador to the United Nations Linda Thomas-Greenfield told a roundtable event, decrying the failure of the UN Security Council to hold a public meeting to end the crisis.

"We are witnessing a humanitarian nightmare ... We cannot let Ethiopia starve. We have to act now," she said, labelling the emergency "man-made".

Ethiopian Prime Minister Abiy Ahmed, winner of the 2019 Nobel Peace Prize, sent troops into the northern region in November to detain and disarm leaders of the Tigray People's Liberation Front, the region's former ruling party.

He said the move came in response to TPLF attacks on federal army camps.

Though he vowed the conflict would be brief, more than six months later fighting continues, reports of atrocities including the widespread use of rape are proliferating, and many leaders are warning of a major catastrophe.

The UN has said that more than 90 percent of the more than five million people in the Tigray region need emergency food aid, and has urgently appealed for over $200 million to scale up its response.

"There is famine now. There is famine now in Tigray," UN humanitarian chief Mark Lowcock said.

"We really do need everybody to step up."

The US has announced $181 million of additional funding to "deliver life-saving food, agricultural supplies, safe drinking water, shelter, health care, and essential services" to those in need in Tigray.

But international aid organisations have complained repeatedly that they are being denied access to all parts of the region by Ethiopian forces and troops from neighbouring Eritrea.

"To avoid humanitarian catastrophe, the entire international community must act directly and indirectly, quickly and robustly," EU crisis management commissioner Janez Lenarcic said.

"A significant scale up of our humanitarian funding response in support of the people affected by this conflict is urgently needed."

The head of the United States Agency for International Development (USAID), Samantha Power, said Ethiopia's military allies "have burned and looted seeds and farm equipment and slaughtered oxen to ensure that the fields lay fallow, so determined are they to eliminate livelihood".

"These same forces have threatened, intimidated, detained and even killed aid workers attempting to feed the hungry," she said.

Power insisted that "we know what is happening in Tigray despite the complex nature of the conflict and the attempts at obfuscation by the Ethiopian government".

"And with that knowledge comes a duty to do all we can to end it," she added.