Medical organisation Medecins Sans Frontieres (MSF) warned on Tuesday that there was a risk of an epidemic of water borne diseases in Muzaffarabad, the quake-devastated capital of Azad Kashmir.
The Paris-based aid group's chief in Islamabad, Isabelle Simpson, said that water supplies could become contaminated because of quake damage, "which is why we worry that that could lead then to outbreaks of other water borne diseases".
"Especially, as very few people have shelter up there, they're crowding into homes and camp type situations; so, there's a lot of potential for health risks," she told AFP.
Aid has begun to trickle into Muzaffarabad after the only roads linking it with the outside world were opened late on Monday but the city, where at least 11,000 are confirmed dead, is still in chaos.
MSF workers who reached the city were still assessing the situation, but "Muzaffarabad itself they consider to be much more destroyed than anticipated," Simpson said.
"It's early days yet, but we have to be very aware that they need at least clean water for drinking purposes," she added.
"At the moment, we're setting up emergency clinics. We still have a lot of people and supplies coming in. It's very early days in terms of access that we can get."
UN Disaster Assessment and Co-ordination team spokesman Andrew MacLeod said aid workers were desperately trying to get supplies of fresh water into the area.