Tens of thousands of foreigners are trying to flee Libya, after clashes between security forces and protesters reportedly left hundreds dead.
Egypt has boosted its military near the border and set up field hospitals, as thousands of its nationals return.
Several countries are evacuating their citizens and oil companies are relocating expat staff.
Correspondents in Tripoli say the capital is calm but there is a sense of intimidation after a night of fighting.
The UN Security Council is currently holding an informal closed session to discuss the crisis. The Arab League will also hold an emergency session.
State TV has reported that Libyan leader Col Muammar Gaddafi will address the country later on Tuesday - it said he would announce "major reforms", but gave no details.
'Crimes against humanity'
Overnight, Col Gaddafi dismissed reports that he had fled amid the unrest sweeping the country, calling foreign news channels "dogs".
Speaking to state TV from outside a ruined building, he said: "I am in Tripoli and not in Venezuela," after rumours that he had flown to Caracas.
Meanwhile, UN human rights chief Navi Pillay said attacks on civilians could amount to crimes against humanity.
In a statement, Ms Pillay condemned the "callousness with which Libyan authorities and their hired guns are reportedly shooting live rounds of ammunition at peaceful protesters".
The BBC's Barbara Plett at the UN says the Security Council meeting is largely procedural, to determine what action can be taken.
The issue is contentious, says our correspondent, as some council members, including China and Russia, see the unrest as purely domestic while western nations are expected to press for strong condemnation of the violence seen in Libya.
Egypt's ruling military council said it had sent reinforcements to the main border crossing, the Salum passage, following a withdrawal by Libyan border guards.
Around 10,000 Egyptian nationals based in their western neighbour are fleeing the violence. Thousands have already returned from Libya since the protests began almost a week ago.
The Egyptian army has set up two field hospitals on the border to deal with the sick and injured.
Egypt says it will send at least four aircraft to evacuate its citizens.
But Foreign Minister Ahmed Aboul Gheit said the airport at Benghazi had been destroyed and there were problems getting flight permits.
"We know there are about one million to 1.5 million Egyptians in Libya, therefore we recommend to our citizens that you stay in your homes, stay off the streets, secure yourselves with water and food," he said.
Meanwhile, unconfirmed media reports said at least 300 foreign construction workers employed by a South Korean company, about 100 of them from Bangladesh, were being held against their will, possibly by protesters, in the eastern port of Darnah.
There are about 50,000 Bangladeshis currently working in Libya.
In other developments:
- China has urged Libya to ensure the safety of its citizens after reports that hundreds of Chinese construction workers in Ajdabiya were forced to flee an armed attack
- Three Turkish ships have been sent to Benghazi to evacuate about 3,000 nationals. A thousand have already been airlifted to safety
- Italy is to send three C-130 air force planes to evacuate its citizens. The former colonial power has about 1,500 nationals resident in Libya
- The US has ordered all non-emergency personnel to leave Libya
- The UK foreign office is advising Britons to leave if they can, although most of the 3,500 resident in Libya are thought to have already left. The remainder have been advised to take commercial flights, but airlines British Airways and BMI have cancelled all flights on Tuesday
- Oil company Royal Dutch Shell says all its expatriate staff have been "temporarily relocated". Italy's Eni and France's Total are also evacuating staff. Spain's Repsol is suspending operations and sending its expatriate staff home.
A BBC correspondent in Tripoli says there is a heavy police presence in the capital; however, the second city, Benghazi, is in opposition control and there is no sign of security forces.
"People have organised themselves to get order back to the city. They have formed committees to run the city," said eyewitness Ahmad Bin Tahir.
Reports that military aircraft had fired on protesters in Tripoli on Monday have been backed up by Libyan diplomats who have turned against the leadership.
But Col Gaddafi's son Saif al-Islam said the aircraft had been used only to bomb army bases which had defected to the opposition.
The BBC's Jon Leyne, in western Egypt, says the regime now seems to be fighting on multiple fronts, trying to put down the protests and fighting a bitter battle against a growing number of army units that have risen up against the Libyan leader.
Reuters reported that the Libyan side of the Egyptian border was now being controlled by opponents of Col Gaddafi armed with clubs and machine guns who were welcoming people across the border.
A growing number of Libyan diplomats around the world have joined many western nations in condemning Col Gaddafi.
Ali Aujali, Libya's ambassador to the US, said the Libyan regime was "shaking".
The time had come to "get rid of it", he told Good Morning America, and urged the US to "raise their voice very strongly".
"Please, please, help the Libyan people. Help them. They are burning. We need the world to stand up by us."
Meanwhile, Libyan state TV denied there had been any massacres, dismissing the reports as "baseless lies" by foreign media.
Foreign journalists work under tight restriction in Libya, and much of the information coming from the country is impossible to verify.
Human Rights Watch said at least 62 bodies had been taken to hospital morques since Sunday, in addition to the 233 people it said had been killed outside the capital previously. Other groups said that figure was much higher.
The violence has helped to push up oil prices to their highest levels since the global financial crisis of 2008.