"They heard the big bang. There was a loud noise, crash, a big bang and then they contacted our national aviation here at the Port Moresby Jackson Airport and then they were informed that it was actually a crash.
"They got there and located the area where the accident occurred."
An Australian man and two Papua New Guinea nationals - the flight co-pilot and a passenger - were killed.
The surviving passengers were taken to hospital in Port Moresby.
Hevilift said in a statement to the Australian Broadcasting Corporation that it would be "conducting a thorough investigation" and was "cooperating with all relevant authorities to determine the cause".
The flight was on its way to the capital from Woitape in Goilala district.
William Seneka, a senior investigator with PNG's Accident Investigation Commission, said weather was believed to have been a factor in the crash.
- Staff reporter