Libya's border with Tunisia is being overrun with migrants, many of them from Egypt, fleeing turmoil in Libya, aid workers say.
A UN refugee official told the BBC that 20,000 Egyptians were stranded and needed food and shelter. Many are sleeping in the open despite the cold.
Some Egyptian refugees staged protests shouting: "We want to go home."
About 100,000 people have fled anti-government unrest in Libya over the past week, the UN estimates.
The BBC's Jim Muir at the Ras Jdir border crossing with Tunisia says the exodus of Egyptian workers from western Libya began on Wednesday, but has been intensifying daily since then.
Liz Eyster of the UN refugee agency (UNHCR) told the BBC that Tunisian authorities were no longer able to cope with the influx.
"They've been accommodating people in shelters, schools and places of their own. But we're now aware of the fact that they're very much stretched and they need the support of the international community."
Monji Slim, the local representative of the Red Crescent, told AFP news agency: "It is a humanitarian crisis, our capacities to take in people are exhausted. The entire world should mobilise to help Egypt repatriate its nationals."
About 7,000 Egyptians have already been evacuated by air, but Ms Eyster said there was a "bottleneck in getting the Egyptians back home".
One stranded refugee said: "All the people here are demonstrating because they want to go to Egypt. All countries are sending aircraft to rescue their people - Turkey, Korea, India, Bangladesh - everyone is arriving and leaving except for Egyptians."
A number of countries have been evacuating foreigners by air and sea.
On Sunday a Greek ship carrying hundreds of migrants - mainly from Brazil, the Philippines, Thailand, Portugal, the Netherlands and Britain - docked at the port of Piraeus near Athens.
The exodus comes as the Libyan leader, Colonel Muammar Gaddafi, battles for political survival in an uprising that began in the east of the country.
At least 1,000 people are believed to have been killed in nearly two weeks of violence in which eastern cities cities have fallen to anti-government forces.
Col Gaddafi is facing the biggest challenge to his 41-year rule, but still controls the capital Tripoli.
However the centre of Zawiya, about 50km (30 miles) to the west, was being held by the anti-government camp on Sunday. Pro-Gaddafi forces are surrounding the city.
"This is our revolution," some demonstrators, quoted by Reuters news agency, chanted.
A number of protesters stood on top of a captured tank while others crowded around an anti-aircraft gun, Reuters added.
US Secretary of State Hillary Clinton said Washington was "reaching out to many different Libyans in the east".
She was speaking on her way to Geneva to meet the UN High Commissioner for Human Rights to discuss the crisis.
Opposition forces that control Benghazi and other eastern cities say they have formed a national council to act as the political face of the anti-Gaddafi movement.
Late on Saturday, the UN Security Council unanimously backed an arms embargo and asset freeze on senior Libyan government officials.
It also voted to refer Col Gaddafi to the International Criminal Court for alleged crimes against humanity.
In a telephone interview with a Serbian TV, he said the sanctions were null and void.
"The people of Libya support me, small groups of rebels are surrounded and will be dealt with," he added.
Col Gaddafi's son Saif al-Islam denied that his father had any assets abroad.
"We are a very modest family and everybody knows that," he told ABC News. "They are saying we have money in Europe or Switzerland... It's a joke."
He also denied widespread reports that Libyan troops and mercenaries had fired on civilians.