Foreigners told Thursday of hellish scenes in Tripoli as they fled the chaos engulfing Libya, with countries worldwide sending planes and warships in a desperate bid to evacuate their nationals.

Anarchy descended on Tripoli airport as thousands of foreigners packed into the terminal to try to escape the widening crisis, with those who managed to leave describing how food and water were running low.

Nearly 20,000 people have also fled Libya by road to Tunisia over the past four days amid the bloodshed sparked by Libyan leader Moamer Kadhafi's attempts to cling to power.

"Libya is descending into hell," said Helena Sheehan, who made it to London Gatwick Airport on the first specially-chartered British rescue flight.

"The airport is like nothing I've ever seen in my whole life," the 66-year-old said. "It's absolute chaos. There's just thousands and thousands of people trying to get out."

Other foreigners told of gunmen standing on roundabouts and getting on buses looking for mercenaries.

Italy, the nearest major European country and Libya's biggest trading partner, warned of a looming "catastrophic humanitarian crisis" as up to 1.5 million migrants flee north Africa.

The logistical challenges were especially acute for Asian countries with more than 150,000 low-paid workers trapped -- including some 60,000 Bangladeshis and 30,000 Filipinos.

China ramped up a massive air, sea and land operation to evacuate more than 30,000 of its citizens, with over 4,000 transferred to the nearby Greek island of Crete on Thursday.

Evacuee Jill Wang, 24, a translator working for a construction firm near Benghazi, said: "We did not go outside the compound, but others who did were robbed by gangs and some got injured. We were really scared and afraid that something worse would happen."

Greek evacuee Costas Koumentakos, from Athens, said: "We had local friends, they saved us. We were afraid because someone could kill you without answering to no one. There is no police, it's anarchy."

Thailand, which has more than 23,000 workers in Libya, said it was making preparations to get its citizens to Malta. India said a passenger ship had arrived to begin evacuating some of its 18,000 nationals to Egypt.

Migrante International, a support group for Philippines workers abroad, said Filipinos had been left to fend for themselves, as Vice President Jejomar Binay planned to fly to the region to review emergency plans.

Egyptians fleeing from Libya described how they had been beaten and tortured after Kadhafi's son accused Egyptians of being behind the uprising.

An evacuee described how Libyan authorities tried to recruit them to help crush the uprising against Kadhafi's 41-year authoritarian regime.

"When we refused, we were beaten up, tortured," said Ashraf Said, from Cairo.

Hundreds of US nationals and other foreigners have boarded a US-chartered ferry in Tripoli but high seas delayed their departure for Malta.

British Prime Minister David Cameron said he was "incredibly sorry" for the delays in getting British nationals home, as the first three planes made it out, carrying adults, children and even a dog.

A British naval frigate carrying around 200 people left Libya's second city of Benghazi. The government said it was looking at all options to rescue people stuck inland in desert camps, refusing to rule out military means.

Germany, which had approximately 160 nationals left in Libya, has sent three warships. Greece sent three troop transport planes to help rescue its 600 nationals in the country.

Turkey evacuated upwards of 6,000 of its 25,000 nationals over three days by air, sea and land.

More than 300 Russian railroad and oil workers and their families returned to Moscow aboard three planes.

"They burned down a police station next to our house. There is a lot of gunfire at night -- rounds of machine-gun fire. We spent sleepless nights," one woman told Russian state television on arrival.

Canada meanwhile had to look for a new plan after a private insurance company cancelled a charter flight secured by Ottawa.

On land, Tunisian security official Colonel Malek Mihoub told AFP that since February 20 nearly 20,000 people had crossed the border at the Ras Jedir post, mainly Tunisians, Egyptians, Chinese and Libyans.

"Some 5,000 people crossed the border Thursday until 1700 GMT," most of them Chinese but also including around 1,000 Egyptians, about 1,000 Tunisians, Moroccans and 200 Libyans, he added.

A convoy of Austrians also reached the Tunisian border, Vienna said.