Vice President Joe Biden once compared it to a “Third World country” — but LaGuardia Airport has become so riddled with homeless that it could now even make some of those nations look good.

The number of derelicts living at the airport has increased dramatically in the past year, turning the main terminal into the city’s most popular de facto flophouse, where they sleep, eat and wash up while competing for space with passengers, according to Port Authority sources.

At least 50 homeless people live inside the airport’s Terminal B, which anyone can get into without passing through security, sources said.

On one night last week, men and women were sacked out on cardboard that they had spread out over warm vents on the floor, a reporter observed. Others were curled up on chairs near Air Canada while televisions blared above their heads. A few were bunched together in couples, but most were solo and kept their distance from others.

Meanwhile, passengers tried to keep as far away as possible while they waited for their flights.

“It has definitely increased — it’s more noticeable on the overnight or midnight tours,” a Port Authority source said.

In the mornings, some of the bums leave for the day, spending their time at soup kitchens or museums around town. But many others hang around 24/7, stealing food from vendors and even getting naked to wash themselves in bathroom sinks, passengers and airport employees say.

“They have taken over,” said one female worker in the food-court area. “You can’t even use the bathroom. They take showers. They hang their clothes on the stalls. They are butt-naked. They think they are in their house.”

A woman who works as a janitor at the airport added, “Sometimes they sleep on the bathroom floor. I clean around them. I don’t touch them. They might get mad, and I don’t want any trouble.”

The bums say they stay in the airport because they feel safer there than they do in city shelters.

“There ain’t nowhere else for me to go that is warm and safe like here,” said a man named Murrell, 49, who has been living in the airport for a few months.

When asked about a recent surge in derelicts, a spokesman for Mayor Bill de Blasio said they were the PA’s problem — even though many clearly come from the city.

“The Port Authority holds a contract with a nonprofit provider to do homeless outreach,” the rep said.

A Port Authority source said, “Our main goal is to provide them services.”

Additional reporting by C.J. Sullivan and Lorena Mongelli