The quake hit about 67 km east of Kainantu and 80 km northwest of Lae in the eastern PNG region, at about 9:45 am local time on Sunday, but was felt some 500 km away in the capital of Port Moresby.
The full extent of damage was not immediately clear as the location of the earthquake was remote. Earthquakes are common in PNG, which sits on the Pacific Ocean's Ring of Fire, a hotspot for seismic activity due to friction between tectonic plates.
While the government gave no death toll, the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) in Asia and the Pacific said that at least four deaths and four injuries had been reported.
One person died in a landslide in Rai Coast, Madang, with three others buried in Wau, Morobe, the OCHA's PNG disaster management team said in a report posted on Twitter.
The regional power grid, internet cables, and the regional highway were damaged, but the airport is operational, it said. Some of the injured were airlifted for immediate treatment.
Papua New Guinea residents shared images and videos on social media of cracked roads, damaged buildings and cars, and items falling off supermarket shelves.
The UN report said people had been injured by falling structures or debris, and there was damage to some health centres, homes, rural roads and highways.
Power infrastructure was damaged in affected areas, causing an outage across the Eastern Highlands.
State-backed communications provider PNG DataCo also reported impact to its undersea cable network, resulting in widespread disruptions.
The US tsunami warning system issued an alert after the quake but later said the danger had passed. There was no immediate threat to Australia, the Bureau of Meteorology said.
In 2018, a magnitude 7.5 quake rocked PNG's remote mountainous highlands, killing more than 100 people and damaging thousands of homes.
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