The men were killed in an ambush in Enga Province, according to the Australian state broadcaster.
A report by local newspaper the Post-Courier said the violence took place on Sunday and was connected to a battle between two tribes.
"This is by far the largest (killing) I've seen in Enga, maybe in all of Highlands as well, in Papua New Guinea," George Kakas, a senior officer in the country's police force, told the ABC.
The Pacific nation is home to hundreds of tribes, many of which still live in inhospitable and remote terrain.
The ABC said the latest violence involved the same tribes that were responsible for clashes that killed 60 in Enga Province last year.
"That is very disturbing the news that has come out of Papua New Guinea," Australia Prime Minister Anthony Albanese said in a radio interview on Monday.
"We're providing considerable support, particularly for training police officers and for security in Papua New Guinea."
