The coal mine is in the heart of Punjab, Pakistan's wealthiest and most populous province, but the labourers mostly come from the poorer neighbouring region of Khyber Pakhtunkhwa.
Although Pakistan has introduced legislation to deal with child labour, the problem is deeply entrenched in society. Nearly 60% of Pakistan's working children are in Punjab province. Children often inherit huge, unpayable debts and are forced to work as bonded labourers. Children working in mines can be vulnerable to dangers such as sexual abuse by older miners.
The donkeys make around 20 trips per day carrying sacks weighing about 20kg each. The work is dangerous with the constant risk of cave-ins. The miners say they do what they can to care for the animals, with their limited resources, but the difficult conditions mean the donkeys' life expectancy is 12-13 years (compared with 30 to 50 years in more prosperous countries).
Reporting by REUTERS.