PORT MORESBY - Flooding in Papua New Guinea's Western Province has affected more than 26,000 people, disaster officials say.
The National Disaster and Emergency Service said heavy rain caused the Fly River system to overflow, inundating villages on the river's banks.
There have been no reports of casualties but thousands of villagers have been unable to return to their homes and are running out of food and water.
NDES director Martin Mose told Radio Australia the number of people affected could increase to 40,000 people once assessment teams have reached more remote areas.
"The actual assessment report that came from the provincial administration did not cover other areas that would give us a better position to plan what type of response we need to take," he said.
Australia has supported the deployment of a joint assessment team and will also help transport relief supplies to the capital Daru this week.