The death toll from the strongest earthquake to strike Papua New Guinea's rugged interior in almost a century has climbed to 31 and will probably rise further, officials says.

Remote villages closest to the epicentre of Monday's 7.5 magnitude quake in the Southern Highlands were buried, killing 13 people, James Justin, a research officer at the Ministry of Petroleum and Energy in Port Moresby said.

Most of the other confirmed fatalities were in or around the provincial capital of Mendi and the town of Tari 40km from the epicentre, where aftershocks continue to be felt and people afraid their homes may yet collapse have been sleeping in their yards.

"Tari is completely shut down," Mark Mendai, head of the district's Development Authority told Reuters.

"All the water tanks have been turned over and at the moment people are suffering a lack of fresh water, all the rivers are dirty," he said. "The runway has some cracks, the district offices are all spoiled, all our roads within Tari are cracked, blocking travelling traffic."

A spokesman from the country's National Disaster Centre said a preliminary damage assessment from the quake, which struck the mountainous Southern Highlands some 560km northwest of the capital, Port Moresby, was still incomplete.

Australia has promised tarpaulins, water purification tablets, and water containers, and despatched a military C-130 transport plane to assist with aerial surveillance.

Pictures showed collapsed buildings in Mendi and residents using shovels to clear away landslides.

That left those injured in villages to the west unable to reach the general hospital, where wards were largely empty except for long-term patients, Wendy Tinaik, assistant to the hospital's director, said.

Miners and oil and gas companies were also assessing damage to their infrastructure, including a 700km gas pipeline that connects to a coastal liquefaction plant, but were hampered by bad weather according to Oil Search Ltd.

Quake damage shut the region's biggest airfield at Komo, built to supply remote Exxon Mobil Corp facilities, though bush airstrips were accessible and Mission Aviation Fellowship evacuated four people to Mount Hagen.