Foreign medics are helping Iraqi special forces personnel treat a growing number of children wounded by intense urban warfare inside the jihadist-held city of Mosul.

Car bombs, sniper fire and booby traps have led to mounting casualties in the east of the city, where advancing Iraqi troops are battling Islamic State group fighters.

Three foreign medics working with the Academy of Emergency Medicine, a Slovakian charity, have teamed up with more than a dozen Iraqi special forces medical personnel to treat wounded civilians and soldiers.

Their sparsely equipped field clinic is set up in an open courtyard on the only route out for fleeing civilians.

Fewer than a dozen green cots are organised into rows, flanked by two ambulances and several crates of gauze, intravenous drips, and other medical supplies purchased with donations to AEM.

Slovakian medic Marek Adamik says most of the casualties he has treated have been from makeshift bombs or sniper fire -- some "directly targeted with head shots."

The charity's country manager, Peter Reed, has just finished tending to the first civilian casualty of the day, a young girl in pink pyjamas with a shrapnel wound to her right leg.

Sporting a thick, strawberry-blond beard, the former US Marine says he came to Iraq in 2015 to join the fight against IS.

But after months without seeing combat, Reed began treating wounded Kurdish peshmerga fighters before "realising there's a need for civilian treatment on the front lines."

- 'Kids are the worst' -

In the space of just three days this week, AEM and Iraqi medics treated a 12-year-old whose right leg was nearly blown off by a mortar round, a scrawny boy hurt when he picked up a mine, and a girl wounded in a car bombing that killed her entire family.

"Kids. Kids are the worst," Reed says, shaking his head.

"Adults and small children stay inside. Kids -- especially boys -- like to go outside and be adventurous."

Wounded civilians are brought to the field clinic in the back of pick-up trucks or on the hoods of armoured Humvees.

It is still too dangerous for their few ambulances to make the one-kilometre (less than one mile) journey to the front line.

AEM staff and Iraqi paramedics work together to stop bleeding or dress wounds, with Reed often barking orders in English that a stocky Iraqi man translates to his colleagues.

Urgent cases -- like the young mortar fire victim -- are transported by ambulance to hospital in Arbil, the Kurdish regional capital, some 80 kilometres (50 miles) to the east.

To relax after treating patients, Reed and fellow American medic Derek Coleman, 27, guzzle down energy drinks and munch on chocolate.

"I ended up here as a foreign fighter, and then I saw there was a need for medical (work)," Coleman, from New Jersey, says.

Lifting his grey baseball cap to pat down his messy chestnut hair, he tells AFP he is bracing himself for a wave of civilian casualties as Iraqi troops push deeper into Mosul.

"Also, if there's no fighting to keep Daesh busy, they may have more opportunity to target civilians," he adds, using an Arabic acronym for IS that its members consider pejorative.

Reed, Coleman, and Adamik spend all day with Iraqi first aiders, then bed down with them in a nearby abandoned home to the sound of intermittent gunfire or shelling.

Even on slow days, they look worn out by the afternoon.

"Less patients mean you remember certain ones much more vividly," says Reed.