Local police believe that the victims were shot dead in an ambush in Enga province, in a major escalation of tribal fighting in the region, according to the report, Xinhua reported.
Authorities were still counting "those who were shot, injured and ran off into the bushes", and believed that more people could have died in the bushes, Royal Papua New Guinea Constabulary Acting Superintendent George Kakas was quoted as saying.
"We presume the numbers will go up to 60 or 65," he said.
"This is by far the largest (killing) I've seen in Enga, maybe in all of Highlands as well, in Papua New Guinea," Kakas said.
It was understood that the tribal fight involves the same tribes that killed more than 60 people last year, ABC News reported.
Facing escalating tribal fighting, Enga province was put into lockdown for several months last year.