Up to 2,500 people would need to be evacuated from Libya's borders with Tunisia and Egypt for the forseeable future in one of the biggest humanitarian evacuations in history, the UNHCR and IOM said today.

The agencies would not give estimates of outflows following the UN Security Council's decision late yesterday that cleared the way for air strikes, but acknowledged that there will be repercussions.

"With the installation of a no-fly zone, we are not clear on what will be the outcome in terms of outfows. However, we see that there will be repercussions on migrants," said Fernando Calado, who heads the International Organisation for Migration's emergency and post-crisis division.

Some 300,000 people have fled Libya since clashes broke out between rebels and pro-regime forces, and many more are expected to leave, the agencies said.

"This is one of the biggest humanitarian evacuations in history," said William Lacy Swing, who heads the IOM, an inter-governmental organisation.

"We expect the needs to continue. People keep arriving at the border. There're different flows according to different circumstances in Libya," said Melissa Fleming, spokeswoman for the UN High Commissioner for Refugees.

"But we're estimating that there'll be at least 1,500 to 2,500 people everyday in need of evacuation for the time to come," she added.

While those who fled initially were mostly migrant workers, UNHCR noted that there has been an increase in the number of Libyans fleeing into Egypt lately.

Some 1,490 Libyans crossed the border on Wednesday.

"The majority of those interviewed at the Egypt border said that they left because of fear of being caught up in fighting. Many mentioned the threats made by the government in recent days to bombard Benghazi," said Fleming.