GENEVA — Hundreds of thousands of people have fled an explosion of ethnic violence in northeastern Democratic Republic of Congo in the past two weeks, the United Nations said on Tuesday, creating a new humanitarian emergency in a region where international agencies are struggling to control an outbreak of Ebola.

The United Nations refugee agency said more than 300,000 people had fled in the face of large-scale clashes between two ethnic groups, the Hema and the Lendu, in Ituri province, which borders Uganda and South Sudan. But officials said that the estimate was conservative.

“The figure could be way, way higher,” Babar Baloch, a spokesman for the refugee agency, said, adding that the violence was preventing aid agencies from gaining access to the area.

The situation had deteriorated in the past week with multiple attacks and counterattacks between the groups, and reports of killings, maiming, sexual violence and kidnapping, Mr. Baloch said.