"UNHCR emergency teams are working with Tunisian and Egyptian authorities and NGOs (non governmental organisations) to support close to 100,000 people that have fled the violence in Libya in the past week," the office of the UN High Commissioner for Refugees said in a statement.
A UNHCR count showed that they were overwhelmingly foreign migrants, mainly Egyptians and Tunisians.
The Red Crescent said earlier that more than 10,000 people fled Libya into Tunisia at the Ras Jedir post on Saturday alone, most of them Egyptians, calling the situation a "humanitarian crisis" as the flow grew.
Before those arrivals, the Tunisian government said Saturday that 40,000 people had crossed from Libya since February 20, while Egyptian authorities accounted for 55,000 people fleeing since February 19, according to the UNHCR.
The refugee agency urged foreign help for Egypt and Tunisia to cope with the exodus.
"We are committed to assisting Tunisia and Egypt in helping each and every person fleeing Libya," the High Commissioner for Refugees, Antonio Guterres, said
"We call upon the international community to respond quickly and generously to enable these governments to cope with this humanitarian emergency," he added.
The UNHCR revealed that its staff had crossed the border from Egypt, and met Libyan police and military nearby who said that they had defected from government forces and were working with local committees of tribal leaders.
Those tribal leaders told the agency there was a need for humanitarian assistance in Libya, "with a critical shortage of food throughout the eastern region, as well as shortages of some medical supplies," it added.
The reports of food shortages echo unconfirmed claims by some Libyan opposition members.
The UN's World Food Programme warned on Friday that Libya's food supply chain was "at risk of collapsing" in the import-dependent country after ships stopped docking and distribution was reportedly hampered by the violence.
UNHCR staff also found 75 people from Bangladesh, Sudan, Thailand and Pakistan without passports in a patch of no-man's land between Libya and Egypt.
The agency said it had reached an agreement with Egyptian border authorities to provide those migrants with shelter, blankets, and food.