More than 3,300 fleeing Iraqis sought help from the government on day nine of its offensive to retake Mosul, the most for a single day so far, a minister said Wednesday.

The number is far short of the hundreds of thousands that aid agencies have been bracing for but the offensive is still in its early stages and many more are expected to flee as troops approach the city itself.

On Tuesday, there was "a big wave of displaced people that is considered the greatest number since the start of the military operation to liberate Nineveh province," Displacement and Migration Minister Jassem Mohammed al-Jaff said in a statement.

"The ministry received and transported more than 3,300 displaced people" to camps, he said.

Most fled homes in Nineveh province, of which Mosul is the capital, but some left from Kirkuk to its west or Salaheddin to its south.

According to a UN tally, 8,940 people have been displaced since the operation to recapture Mosul from the Islamic State group began on October 17.

The number so far is a drop in the ocean compared with the more than three million people who have been displaced by violence in Iraq since the start of 2014.

But the UN refugee agency expects tens of thousands to flee in the coming days and is establishing camps with a total of 30,000 tents, enough to accommodate 150,000 people.

Top US general visits key hub in fight for Mosul
Qayyarah, Iraq (AFP) Oct 26, 2016 - A top US Army general on Tuesday flew in to an airbase south of Mosul that will prove vital in Iraqi forces' offensive on the Islamic State-held city.

US Army General Joseph Votel, who heads the military's Central Command, arrived at the base, which boasts a newly repaired runway, on a cargo plane to see the facility and receive an update on the battle for Mosul, now in its second week.

Qayyarah West, located about 60 kilometres (40 miles) south of the city, has been resurrected after jihadists smashed it to pieces when they seized much of northern Iraq in 2014.

A dusty wasteland of twisted reinforcement bars, booby traps and smashed buildings until only a few months ago, much of the airfield has been restored by US Air Force engineers and turned it into a key military installation for Iraqi security forces pushing north.

IS were chased from the area around Qayyarah in July, and now about 500 Americans are stationed here, along with the Iraqis and other members of the US-led anti-IS coalition including France and a small British team.

Votel's C-130 cargo plane touched down in total darkness, one of the first fixed-wing aircraft in years to land at the base.

"This is where supplies will come into, it's where Iraqi forces will come into. Being able to sustain the fight for the Iraqi forces will be critical, and this airfield will play a very important role," Votel told reporters travelling with him.

The four-star general was accompanied by Lieutenant General Stephen Townsend, who heads the coalition effort supporting and training Iraqi security forces and Kurdish peshmerga units as they attack IS.

They said the campaign to recapture Mosul is continuing apace, but cautioned IS defences will grow stronger the closer Iraqi forces get to the city.

The Islamic State group "has used an extraordinary amount of indirect fire -- mortars, artillery and rockets -- and an exceptional number of VBIEDs over the last eight days," Townsend said, referring to vehicle-borne suicide car bombs.

IS fighters have refined their use of suicide bombers in recent days, he said, and are hiding custom-armoured cars behind walls and inside structures.

Jihadist drivers then race these vehicles toward advancing Iraqi security forces at the last minute, instead of attempting to drive across open plains where they can be quickly destroyed by missiles.

- French artillery -

Qayyarah is also being used to stage artillery units and HIMARS rocket launchers that aim north to help clear the way for Iraqi troops moving toward Mosul.

Early in Votel's visit, the base reverberated with the sound of a French howitzer blasting out of the base.

Military officials say the Mosul operation is going quicker than planned in some places, and on Tuesday units of Iraq's elite counter-terrorism force were just six kilometres (four miles) from Mosul, where IS two years ago proclaimed its "caliphate".

As forces have closed in on Mosul, IS has set fire to oil wells, torched tyres inside the city and set up a defence system around it that includes burning oil trenches to blind their enemy's air and satellite assets.

Soldiers at Qayyarah said some of them have worn respiratory masks, especially after IS set a sulphur plant ablaze.

But by Tuesday night, shifting winds meant the air at the base was reasonably clear.

What will become of the base after the presumed defeat of IS remains to be seen.

US officials stressed that whether the United States will maintain a military presence there is for the Iraqis to decide.