At least 28 people were killed when a small passenger plane went down in stormy weather in a heavily-forested area of northern Papua New Guinea.

The two pilots, one Australian and one from New Zealand, survived, as did two passengers, a Papuan and a Chinese.

The plane, a twin-engine Airlines PNG Dash 8, was flying from the mountain gateway city of Lae to coastal Madang on Thursday. Most of the people on board were family members of local university students, going to a graduation ceremony.

The plane went down in the Gogol River, about 20 kilometers south of its destination.

Papuan officials say an investigation is underway.