Geoscience Australia's website said the quake was near Lae, the second largest city, and that tremors had been felt 225 kilometres away in Port Moresby, the capital.
A correspondent for Australia's AAP news agency in Port Moresby said the windows of Parliament House shook for more than a minute but that there was no damage.
Geoscience Australia senior seismologist Clive Collins told AAP that Wau, with a population of about 5,000, was only 20 kilometres away from the centre of the quake.
"There're no reports of people losing lives yet," he was quoted as saying.//DPA