At least 20 members of a remote cave-dwelling Philippine tribe have been killed in an outbreak of diarrhoea, the health department said on Wednesday.
Most of the fatalities were children aged under five from the nomadic Palawanon tribe, according to Dr Manuel Mapue.
The full extent of the outbreak, which began on March 27, is unknown as the tribe, based in the mountains of the western island of Palawan, is extremely isolated.
"Most of the casualties did not seek consultations from health officers because they are tribesmen living in caves in the mountainous part of the district which is a five-hour walk from the nearest village," Mapue told AFP.
He said there have been 90 recorded cases of diarrhoea so far but there may be even more undocumented cases.
The tribe may have come across a contaminated stream during their nomadic travels, leading to the outbreak, said the doctor.
The tribe does not boil their drinking water or use chlorine tablets, making them even more vulnerable, he added.
Mapue said his team will go to Palawan island on Thursday to check the water sources for contamination and test members of the tribe.
Anthropologists say about 30,000 people speak several dialects associated with the Palawanon tribe, whose members live in isolated communities scattered in the interiors of Palawan.