The UN has delivered urgent rations to the town which had been “inaccessible” to aid workers since it was captured by militants in June 2014.
Qarrayah, located on the Tigris, was retaken by Iraqi forces on August 25 following a three-day operation backed by US-led coalition airstrikes.
"The people of Qayyarah... are suffering extreme hunger with scarce access to food supplies," said Sally Haydock, the UN World Food Programme country director for Iraq.
WFP said in a statement the food delivered in the past week included dates, beans and canned food as well as rations containing lentils, rice, flour and vegetable oil, enough to last for a month.
The town is "in a dire state" with "black smoke" rising from oilfields around it that were set ablaze by the extremists during fighting, WFP added.
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"Safe drinking water, electricity and medical services remain nearly impossible to access," it added.
The UN refugee agency UNHCR warned last month that a Mosul offensive could displace another 1.2 million people.
Around 3.4 million people have already been forced to flee their homes in Iraq by conflict since the start of 2014.
WFP said it was “scaling up its food assistance in Iraq ahead of the Mosul offensive but “urgently” needed $106 million to aid displaced families until the end of 2016.