An initial earthquake of 7.6 magnitude struck the Markham Valley at 9:46am on Sunday, followed by a 5.0 magnitude earthquake 70 km north an hour later, Commissioner of Police David Manning said in a statement on Monday.
The two earthquakes were reported at a depth of 90 km and 101 km underground, he said.
Significant damage to buildings and roads and landslides were reported in Morobe, Eastern Highlands and Madang provinces.
"Sadly, seven people have been confirmed dead as a result of these landslides. Three in Kabwum District and three in Wau Town, Morobe Province, and one in Rai Coast, Madang Province," he said.
"This was a significant earthquake, however it occurred deep below ground level and this meant damage was less than if the epicentre had been closer to the surface," he added.
Aviation company Manolos Aviation organised medical evacuations from Kombul village in Kabwum district.
"Half of the mountain is gone," said Manolos Aviation public relations officer Erebiri Zurenuoc, who was at the scene in Kombul.
A National Command Centre has been established by the government, and a COVID-19 hotline has been repurposed for the public to offer information on earthquake damage.
The regional power grid, internet cables, roads and highways had been damaged, Manning said.
In Eastern Highlands province, there was damage to the University of Goroka and reports of injuries to students, he said. Engineers are assessing damage to the Yonki Dam that has caused power outages.
In Madang province, there were multiple injuries as buildings and houses were damaged, and one death was reported on the Rai Coast, he said.
He warned of a significant risk of aftershocks.
