An ongoing joint Iraqi operation against the Islamic State group south of the city of Mosul could displace 30,000 civilians in the coming weeks, the UN refugee agency warned Tuesday.

Iraqi federal and Kurdish forces backed by the US-led coalition against IS launched the offensive in March in the province of Nineveh, of which jihadist-controlled Mosul is the capital.

These forces are still at least 50 kilometres (30 miles) south of Iraq's second city but the fighting there has been forcing thousands of civilians from their homes.

An existing camp in Debaga, which lies east of Makhmur -- the main staging ground for that operation -- already hosts around 8,000 people, the UN High Commissioner for Refugees said.

It said it opened a new camp on the grounds of a football stadium in Debaga this week "in response to increasing numbers of newly displaced families".

"As many as 30,000 newly displaced individuals may arrive in Makhmur over the coming weeks as the military offensive continues," the UNHCR said in a statement.

"The newly built facility will help to ease some of the overcrowding that we have seen since the latest fighting began," said Fred Cussigh, head of UNHCR's field response unit in the area.

The aid community is concerned that a massive military operation to retake Mosul will cause displacement on a scale that Iraq cannot handle.

According to some estimates, up to one million civilians may still live in Mosul, which has been IS's main hub in Iraq since it took over the city in June 2014.

At least 3.4 million people have already been displaced in Iraq since the beginning of 2014.