Thousands of people have fled the Mosul area in northern Iraq, where an offensive is underway to drive out the Islamic State (IS) group.
The charity Save the Children said on October 19 that 5,000 people had crossed the border into Syria in the last 10 days and arrived at the Al-Hol camp.
"Conditions there are among the worst we've seen, and we expect thousands more people to be on their way soon," said Tarik Kadir, head of the group's response to the Mosul crisis.
The UN said the camp received more than 900 people in the last 24 hours and is expecting a further 3,000 people who were dropped off by smugglers and are being cleared by security.
Al-Hol, which was built to house 7,500 people but currently holds 9,000 refugees, is being expanded to eventually take in 50,000 people.
Camps are also being built in the south, east, and north of Mosul in preparation for a flood of civilians fleeing the city, where up to 1.5 million people are thought to be living, with up to 5,000 IS militants.
Meanwhile, the chief of the Russian military's General Staff has expressed concern that IS extremists holed up around Mosul might escape to Syria.
"It's essential not to chase the terrorists from one country to another but to destroy them on the spot," General Valery Gerasimov said in an October 19 statement.
Gerasimov also said the Russian military was using both space and air reconnaissance systems, including drones, to "monitor the situation in the Mosul area."
Iraqi troops and Kurdish fighters have taken back control of a string of villages since their offensive to retake Mosul started on October 17.
WATCH: Iraqi, Kurdish Forces Liberate Villages Outside Mosul
Based on reporting by AP, Reuters, AFP, Interfax and the BBC