A rapidly increasing flow of people is pouring out of western Mosul, fleeing fierce battles between Iraqi security forces and ISIL fighters, as medical workers warned that women and children have been exposed to toxic gas near the city.

Iraq's interior ministry said on Friday that 14,000 people fled the northern Iraqi city on Thursday alone, the largest wave of internally displaced people (IDPs) since a US-backed operation in west Mosul was launched on February 19.

The total number of IDPs who fled western Mosul since the start of the military push has reached 46,000, the ministry said.

The announcement followed a previous statement by the United Nations warning that around 4,000 civilians were fleeing the city, ISIL's last major urban stronghold in Iraq, each day.

Al Jazeera's Stefanie Dekker, reporting from a refugee camp in Khazer, east of Mosul, said that IDPs there cited the "intensity of coalition air strikes" as one of the main reasons for leaving their homes.

"People in the camp who just arrived explained how terrifying the situation was on those frontlines," she said.

"It's a desperate situation for these people; they are being moved across the country to different areas to be housed.

"Aid agencies are warning that they expect the numbers to rise, particularly because west Mosul is densely populated and the fighting has not even reached those areas."

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The quickening exodus comes as the International Committee of the Red Cross said on Friday that seven people were receiving treatment for exposure to chemical agents near Mosul.

"During the past two days, the hospital has admitted five children and two women showing clinical symptoms consistent with an exposure to a blistering chemical agent," Robert Mardini, the Red Cross Middle East director, said in a statement, referring to a facility near Mosul.

The symptoms include blisters, redness in the eyes, irritation, vomiting and coughing.

"The use of chemical weapons is absolutely prohibited under international humanitarian law. We are deeply alarmed by what our colleagues have seen, and we strongly condemn any use of chemical weapons, by any party, anywhere," Mardini said.

The statement did not specify whether the seven were wounded in one or more attacks, how the chemical weapons were delivered, or who was responsible.

ISIL, which holds the majority of west Mosul, has periodically used rudimentary chemical weapons in the course of its more than two-year war with Iraqi forces.

Fierce fighting

The push for western Mosul began after the eastern half of the city, which is separated from the ISIL-held west by the River Tigris, was declared "fully liberated" in January.

Mosul fell to ISIL in the summer of 2014, along with large expanses of northern and western Iraq.

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The Iraqi military believes several thousand fighters, including many who travelled from western countries, are hunkered down in Mosul among the remaining civilian population, which aid agencies estimated to number 750,000 at the start of the latest offensive.

The fighters are using suicide car bombers, snipers and booby traps to counter the offensive waged by tens of thousands of Iraqi troops, Kurdish Peshmerga fighters and Iranian-trained Shia paramilitary groups.