A 7.5-magnitude quake struck the Pacific nation's mountainous interior on February 26, burying homes and causing landslides, making it hard to reach isolated villages.
Police said the toll had now reached 125, up from 100 last week, as more news filtered in from remote communities.
"From the reports received at the command centres, 45 have died so far in the Southern Highlands and in Hela province 80 people are confirmed dead," the Royal Papua New Guinea Constabulary said in a statement.
It added that 15,000 people had been displaced in the Southern Highlands and at least 20,000 in Hela, with many now in temporary shelters. Schools remain closed.
While aid is finally reaching remote areas, doctors warned that public health issues must also be urgently addressed, with fears disease will kill even more people.
Earthquakes are common in PNG, which sits on the so-called Pacific Ring of Fire, a hotspot for seismic activity due to friction between tectonic plates.