Debaga is one of five camps the UNHCR — the UN’s refugee agency — has opened and has the capacity to shelter 45,000 people, the agency says.
The camp, located 40 km (25 miles) south of the Kurdish capital of Erbil, is already home to more than 30,000.
One recent arrival told Reuters they had faced a very difficult route to safety with “mines and challenges”.
The camp manager said his team was “operating beyond our capacity”.
There were no figures immediately available for the numbers of arrivals since the beginning of the military operation, launched on Monday (October 17).
Iraqi Prime Minister Haider-al Abadi said on Thursday the operation was doing faster than planned.
Mosul is the last big city stronghold held by Islamic State (ISIS / Daesh / ISIL) in Iraq.
The recent arrivals in Debaga were from Howeija and Shurkat regions, south of Mosul.
The United Nations has said the battle would require the world’s biggest and most complex humanitarian effort, which could leave up to one million people homeless and see civilians used as human shields or even gassed.
There are already more than three million people displaced in Iraq as a result of conflicts involving Islamic State (ISIS / Daesh / ISIL) and up to 100,000 Iraqis may flee Mosul to Syria and Turkey.
In Mosul itself, medicine is in short supply and food prices have risen sharply.
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