Aid workers warn a humanitarian disaster is unfolding in Fallujah, following a civilian exodus from the Iraqi city.

Photo: AFP

About 80,000 people have fled during a four-week government offensive to drive back Islamic State (IS) fighters, the United Nations said.

It said another 25,000 civilians are likely to do the same.

Prime Minister Haider al-Abadi has declared victory over the jihadists after troops reached the city centre, but shooting, suicide bombs and mortar attacks continue.

Nasr Muflahi from the Norwegian Refugee Council (NRC) said aid workers were struggling to provide food, water and medicine to people sleeping in the open in hopelessly overloaded camps outside the city.

"The overwhelming number of people that have come out of Fallujah has actually overwhelmed our ability to respond to the people in need.

"We implore the Iraqi government to take charge of this humanitarian disaster unfolding on our watch," he said.

Iraqi government forces have succeeded in retaking most of Fallujah, but fighting continues in some parts of the city, which is just 50km west of Baghdad.

Photo: AFP

Many of those who fleeing the fighting have been forced to sleep in the open, and spend their days under the sun in temperatures set to reach 47°C in the next few days.

Camps are already overflowing with escapees who trekked several kilometers past Islamic State snipers and minefields.

"People have run and walked for days. They left Fallujah with nothing," said Lise Grande, U.N. Humanitarian Coordinator for Iraq. "They have nothing and they need everything."

Aid supplies are running dangerously low in overcrowded conditions. One newly opened camp, Amiriyiah al-Fallujah, has only one latrine for 1800 women, the NRC said.

Prime Minister Haider al-Abadi's government has already been struggling to meet the needs of more than 3.4 million people across the country who have been displaced by conflict.

Photo: AFP

The Islamic State's news agency, Amaq, reported on Sunday (local time) that about 50 Iraqi troops had been killed and four army vehicles destroyed in "fierce fighting" with IS fighters near Fallujah General Hospital in the north-east of the city.

Several civilians have been killed by militants while attempting to escape, including, on Monday, a two-year-old boy who was being carried by his mother.

Some residents were reportedly used as human shields by IS to slow the advance of government forces, who are being backed by air strikes from the US-led coalition.

IS militants had captured the northern city in January 2014 and held it for longer than any other city in Iraq or Syria - before the Iraqi army launched an operation to retake it.

-BBC / Reuters