The earthquake, which struck shortly after midnight local time, was the most severe aftershock in an area badly damaged by a magnitude 7.5 quake that flattened villages and caused landslides, killing at least 55 people.
"I have just received reports that 18 people were killed last night," William Bando, Hela Province administrator told Reuters.
"It appears Hides was hardest hit. We haven't heard about potential casualties there yet, but it is a big village with many people."
Landslides, blocked roads, cracked airstrips and damaged telecommunication links have hampered efforts by authorities to assess the death toll and deliver supplies to the more than 150,000 people that agencies estimate are in need of aid.
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