In a Pakistan paediatric ward, a chorus of infant coughs and straining lungs is the toll of a frigid winter, compounded by choking smog and lagging vaccination rates.

"Please pray for him," the mother of four-month-old pneumonia patient Ibrahim begs a nurse in Lahore, delicately arranging a blanket around ventilator tubes piping air in and out of his heaving chest.

The eastern megacity is blanched every winter by smog levels rated among the worst in the world.

Rain usually brings respite, soaking up pollution particles, but Pakistan has endured an unusually dry and cold winter -- making children vulnerable to respiratory infection, doctors said.

In January alone, more than 18,000 pneumonia cases and nearly 300 fatalities were registered in eastern Punjab province.

Around half of childhood pneumonia deaths are associated with air pollution, according to UNICEF.

The provincial government extended school holidays, clipped classroom hours and mandated face masks in a bid to shield children.

The Children's Hospital in Lahore has nevertheless admitted hundreds of cases every day.

Outside the main building of the 1,300-bed facility, Rashid Liaquat sits with his three-year-old son Mohammad Ali, who developed a high fever five days ago.

When 31-year-old Liaquat heard his son fighting for breath in his sleep he rushed him to the clinic where he was diagnosed with pneumonia.

"The wheezing sound really scared me. I did not know it was pneumonia but I was sure something was really wrong," Liaquat said.

The first question doctors asked him was whether Ali was fully immunised, which he was, spurring his road to recovery. But many are not, according to senior doctor Junaid Rashid.

"We feel uncomfortable when a child comes to us with the disease and he has not been vaccinated," the 55-year-old medic said.

Pakistan offers free jabs for respiratory disease at six, 10 and 14 weeks of age.

But Islamabad has long grappled with the challenge of increasing vaccine uptake in a nation where misinformation is rife and some fringe clerics declare it un-Islamic.

Premature births and stunting caused by malnutrition are also prevalent, weakening children who are then easy prey for pneumonia.