Health workers are braving freezing temperatures this week to administer polio vaccinations in Pakistan-administered Kashmir after cases surged nationwide last year.

Pakistan and neighbouring Afghanistan are the only countries where polio is endemic, and militants have for decades targeted vaccination teams and their security escorts.

A police officer guarding polio vaccinators in the northwest was shot dead by militants on Monday, the first day of the annual campaign that is due to last a week.

In Kashmir, health worker Manzoor Ahmad trudged up snowy mountains as temperatures dipped to minus six degrees Celsius (21 degrees Fahrenheit) to administer polio vaccinations in the region.

"It is a mountainous, hard area... we arrive here for polio vaccination despite the three feet of snowfall," Ahmad, who heads the polio campaign in Pakistan-administered Kashmir, told AFP.