The Airlines PNG Dash-8 was flying from the mountain gateway city of Lae to coastal Madang when it crashed around 5pm local time (0800 GMT), killing a number on board, the Accident Investigation Commission said.
"There has been an aircraft accident here involving Airlines of Papua New Guinea," AIC investigator Sid O'Toole told AFP.
"There were 32 people on board and there are some survivors and some fatalities."
O'Toole said there had been "adverse weather around the area at the time" but could not confirm witness reports of a violent and sudden storm ahead of the crash, 20 kilometres south of Madang near the mouth of the Gogol river.
Most on board were believed to be the families of local students due to graduate this weekend and only four were believed to have survived, according to media reports, which also cited witnesses seeing flames.
The inland site had been secured by police and ambulances had arrived on the scene, with local emergency authorities and hospitals on standby and an air crash investigator already on the ground in Madang, O'Toole said.
Australian transport accident officials had also been contacted for assistance, he added.