The President of the autonomous Papua New Guinea region of Bougainville, Ishmael Toroama, says hundreds of people have been displaced by the eruption of Mt Bagana.
The 1800 metres mountain, in central Bougainville, began erupting nearly two weeks ago.
Toroama said all water sources were contaminated, leading to waterborne diseases.
He said 19 primary and elementary schools have been affected and they have all been shut down temporarily.
The president said ensuring there was sufficient food, water and medical supplies for the people is the top priority.
“We have deployed our health officials to conduct an environmental assessment to ascertain the suitability of setting up care centers at Torokina and Wakunai respectively.
“Natural disasters are volatile and may change at any moment. The welfare of our people is far greater than any one person who chooses to be ignorant in these circumstances,” Toroama said.
The Rabaul Volcanological Observatory said while the summit area remained obscured, there had been a pyroclastic flow, but that this was small and confined to riverbeds.
This flow includes lava, ash and hot gases, and it means rivers originating from the volcano were contaminated.
Toroama has thanked the Minister for Internal Security Peter Tsiamalili Jnr and the Minister for Information and Communication Technology Timothy Masiu for their responses to the disaster after they made funding available for supplies.
He added that “the Australian Government has assured me that they will respond to the situation should it escalate”.