The very shallow quake was only 2 kilometres deep and 93km southwest of Porgera in the Enga province, the EMSC said.
Earthquakes are common in Papua New Guinea, which sits on the Pacific's "Ring of Fire", a hotspot for seismic activity due to friction between tectonic plates.
This is the second powerful earthquake to hit the region in the last few months.
PNG declared a state of emergency following a magnitude-7.5 quake on February 26 that devastated parts of Highlands Region.
Local authorities said more than 50 people were killed in the February earthquake.
In towns nearest to the epicentre of the earthquake, "there were buildings or structures that sustained damage to them and the powerlines as well," said the director of the National Disaster Centre, Martin Mose.
"There were a couple of poles that actually gave way and there were trees being uprooted."
Mr Mose said local people were terrified by the continuing aftershocks after February's quake.
"I was on the ground when one hit and I can just see the evidence people start running and screaming everywhere and it shows me that they're still very much scared of what actually happened," he said at the time.
The Australian Government offered $200,000 for aid and its first shipment of supplies — tarpaulins, water containers and purification tablets — was flown to the highlands on March 2.
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