Story highlights About 40,000 Yazidis are hiding in the mountains of northwest Iraq

The Yazidis fled after ISIS fighters stormed the area they call home in Iraq

"I don't think we can ever go home," one survivor tells CNN's Ivan Watson

An estimated 100,000 Christians have fled to Irbil in recent days

No food. No water. And as they pass the hours in the scorching summer heat, no escape for 40,000 desperate people hiding in the mountains of northwestern Iraq from the killers surrounding them on the ground below.

When fighters from ISIS, which refers to itself as the Islamic State, stormed Sinjar over the weekend, the Yazidi minority who call the area home fled into the nearby mountains in fear of their lives. Some of them didn't make it.

"We heard sounds of mortars and in the morning they (Islamic militants) entered Sinjar," Zahra Jardo, a Yazidi woman who escaped the violence, told Reuters. "So we fled to the mountains, and those who stayed there are now suffering from thirst. They have no water. They also took girls and raped them. They said that Yazidis have to be converted to Islam."

The Yazidis, descendants of Kurds who follow an ancient pre-Islamic religion, have only bad options: continue to hide in the Sinjar Mountains and die of thirst, or come down from the mountains and be massacred by the radical Sunni militants who are forcing Islam or death on the communities they overtake as they sweep across Syria and Iraq.

Dozens of children have already died from dehydration. Women have been taken as slaves, and hundreds of men have been slaughtered. Now many observers fear full-blown genocide if the Yazidis' pleas for help aren't answered soon.

The only Iraqi lawmaker who represents the Yazidis broke down this week as she described the plight of her people in an Iraqi parliamentary session.

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"There is a collective attempt to exterminate the Yazidi people. ... Let's put our political differences aside and work together as human beings," Vian Dakhil pleaded to her colleagues through tears. "In the name of humanity, come to our rescue, come to our rescue."

But that rescue is nowhere in sight, at least for now. Kurdish fighters, known as Peshmerga, are battling to retake the town of Sinjar from ISIS, but they're being stretched almost to the breaking point by a second ISIS offensive to the east that has driven 200,000 Iraqis from their homes in a mere 48 hours.

They fled in anything with wheels, thousands of trucks and cars tearing through the northern Iraqi desert toward the gates of the Kurdish capital of Irbil. The city has been a refuge of safety during the decade-long war that has ripped the country apart. Now that ISIS militants have captured Kurdish towns just 35 miles away, no one is sure how long things will stay that way.

Everyone arriving in Irbil told the same story. Peshmerga soldiers -- badly outgunned by ISIS fighters equipped with American weapons and armored vehicles stolen from Iraq's army -- withdrew from their towns and villages amid the onslaught, and families had just minutes to pack and leave their homes.

"I'm too scared," a visibly shaken 22-year-old university student named Andros told CNN's Ivan Watson in Irbil. "There were a f**king thousand cars, and my father drove a car for six hours -- three hours in the dust and three hours on the road. When we were in the dust, we couldn't see anything, just cars running away. We didn't know where we were going.

"Those people are not people, they're monsters. They're not even monsters; monsters are better. I don't think we can ever go home. It's finished."

Andros and his family are now sleeping in what amounts to a construction site on the outskirts of Irbil. Children mill around their grim new residence, and clotheslines ring the gray, concrete columns inside the unfinished building where hundreds of displaced Iraqi Christians have taken shelter.

Across the street from the unfinished building, refugees pack St. Joseph's Church. Mothers comfort young children as elderly women curl up on the floor and in the chapel's pews. Outside, people look for pockets of shade to protect them from the 100-degree heat.

An estimated 100,000 Christians have poured into Irbil in two days. The Christians whom CNN's Watson spoke to say they are ready to leave Iraq for good. There's no future for them here, they said, and they don't think they'll ever be able to go home again.

"They took our homes, our money, everything," Andros said.

Local officials are trying to make sure everyone has food and water, but they're overwhelmed on all fronts. The United States and Britain have pledged additional humanitarian support, and the United Nations said it was preparing a humanitarian corridor to allow Iraqis to flee the chaos in the north.

The Kurdish leadership had promised an alarmed public that the Peshmerga would be able to protect Irbil from the militants nearing the city's gates, while at the same time begging the United States to intervene militarily against ISIS.