A centuries-old salt mine in Pakistan is offering experimental asthma therapy, attracting patients from all over the world.

Khewra, billed as the world's second largest salt mine, has for centuries extracted the crucial mineral for export and has become a tourist attraction complete with a salt mosque and an electric train.

Now, the mine is cashing in on salt therapy, already a draw in the salt mines of eastern Europe and a synthetic clinic in Britain.

Clinics claim that asthma patients and sufferers of other respiratory illnesses benefit from inhaling antibacterial salt particles in a sterile environment, helping loosen mucus and clear the lung passages.

"We don't use any medicine, because the asthmatic allergy patients recover through the air, so we provide them an environment in which their breathing can improve," said Akhlaq Bukhari, head doctor at the Khewra clinic.

Although there have been few clinical studies, salt caves are seen by some as a therapeutic alternative to drugs and there are natural and synthetic salt caves springing up all over the world.

While other clinics offer treatment for bronchitis, cystic fibrosis, and even ear infections, Shah says the Khewra clinic only treats patients whose asthma is triggered by allergies.

"I have come here all the way from Canada. I could not recover there through medicine, but I am feeling better since my arrival here," said Naeem Shamsher, a civil engineer from Canada.