Violence and insecurity is reported spreading in Ethiopia beyond the conflict-torn Tigray region as people flee its major city of Mekele, UN humanitarians have said.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) on Wednesday said it has been receiving reports of the worsening situation "after the relocation of security forces to Tigray, with several reports of clashes and attacks in other places."

The government delivered a 72-hour ultimatum on Sunday to the Tigray People's Liberation Front (TPLF) to surrender.

Published reports said the Ethiopian National Defense Force (ENDF) has surrounded Mekele, Tigray's major city with a population of about 500,000 people.

Nearly 42,000 people already have fled Ethiopia into Sudan, the humanitarian office said in a release.

Also, more than 95,000 people are estimated to be newly displaced in the Southern Nations, Nationalities, and Peoples' Region (SNNP), following clashes reported last week, OCHA said.

Food, water and shelter are urgently needed in the region. Most of the displaced people are in open spaces after public buildings, schools and facilities reportedly were burned in recent violence.

The SNNP region is in Ethiopia's south, separated from the northernmost Tigray region by other regional states.

"We are worried about this," Farhan Haq, deputy spokesman for UN Secretary-General, Antonio Guterres, told reporters in a regular briefing.

"Our humanitarian colleagues are already trying to deal with the situation involving people fleeing from Mekele and our worries (are) that the situation could get worse."

The federal government's military operation began Nov. 4 in Tigray following the TPLF's attack on the ENDF Northern command base, a division stationed in the region for over two decades and based in Mekele.

The Ethiopian government on Tuesday said a "large number" of Tigray Special Forces and the militia were surrendering as part of the Sunday ultimatum.