Some 6,000 patients have been admitted to Kabul hospitals in the past three weeks with diarrhoea-related diseases and three have already died of cholera.
A special task force has been set up to tackle what health officials fear could become a crisis with the disease "spreading like wildfire".
Extra chlorine is being added to Kabul's water supplies, already under pressure from growing numbers of returning refugees, to disinfect the city's drinking water.
Kabul's war-damaged infrastructure and sanitation problems threaten the population with the dangers of an epidemic breaking out if measures are not taken swiftly.
Raising awareness
WHO spokeswoman Loretta Girardet said: "Cholera can spread like wildfire if control measures are not urgently implemented."
Cholera is known to occur in parts of Afghanistan from time to time, and it is estimated that 85,000 children die of it every year.
But there have been few reports of an outbreak of this water-borne disease in the capital city.
A dense and growing population, limited facilities, and the political and economic importance of the city to the reconstruction of the country makes the prospect of an outbreak here especially worrying.
Health officials and aid staff are working together on a health education campaign using radio, television, mosques and schools to raise awareness of the problem and reinforce preventative measures.
The cholera task force, which co-ordinates all cholera-related activities, is reviewing progress on a weekly basis.