In the wake of Cyclone Tomas, which tore through the north and east of Fiji last week, UNICEF says it is hurrying to treat a group with a serious disease, thought to be typhoid.
UNICEF's deputy representative for the Pacific, Tim Sutton, says a government health worker has discovered 16 people in one place, in Labasa, with bloody diarrhoea.
He says tests are underway, but it's thought the illness is typhoid, shigella or cholera.
"It means that the disease has spread very quickly amongst a group of people. It means that transmission is happening, and if it's happening one place, it's very very likely it is happening over a wider area. This is the first indicator of something we have been trying to signal and the Ministry of Health here has been trying to signal, for at least a week."
Tim Sutton says rehydration solutions and water purification kits are being sent to the town.
Fiji has already experienced over a hundred cases of typhoid so far this year.