Aid workers are urgently trying to improve water supplies and sanitation at the cramped refugee camps where the survivors fell sick in the devastated Muzaffarabad, WHO Technical Officer Rachel Lavy told AFP.
"In one camp we visited yesterday there were 55 cases of diarrhoea and there are so many spontaneous camps that we believe there are hundreds of others," Lavy said as she headed to one of the camps.
"Acute watery diarrhoea fits very closely with the definition of cholera. That is one of the things it can be," Lavy said, adding, however, that there were other waterborne diseases that could cause similar types of diarrhoea.
"We are treating it as suspicious, but we don't have laboratory guidance at this stage," she said.
The United Nations has repeatedly warned it is racing against time and a shortage of international aid cash to prevent a possible second wave of deaths from disease, cold and hunger after the October 8 disaster.
"The WHO is saying that even if the laboratory diagnosis is not confirmed, these cases should be taken as seriously as if they were cholera," UN Spokeswoman Amanda Pitt said.
She said a small number of acute diarrhoea patients had been reported from other towns in the quake zone in recent weeks and that outbreaks of disease were "not unexpected". Lavy said there were 40 other cases recorded last week in Chiniari, a small town in AJK.
British charity Oxfam warned last week that the squalid conditions in the camps could kill thousands of people, far exceeding the toll in remote villages that have been the focus of aid efforts so far.
More than 7,000 cases of diarrhoea - not all of them acute - and 8,000 cases of respiratory disease had been reported in the quake zone, Pakistani Health Ministry official Anwar Mahmood told AFP. "We are monitoring the situation daily," he said.
Acute diarrhoea can be fatal if it is not treated aggressively and immediately, Lavy said.
"It can dehydrate an adult within a few hours," she added. "If you get watery diarrhoea you need to treat it aggressively with massive re-hydration, isolation, ensuring clean water and sanitation to prevent contamination." But she said that curbing the spread of illness was especially difficult in the densely populated tent camps that have sprung up in Muzaffarabad.