Unstable terrain, remote locations and damaged roads are hampering relief efforts in Papua New Guinea after more than 670 people were feared killed in a landslide last week in the Pacific nation's north, the United Nations said on Monday.

Emergency crews, led by Papua New Guinea's (PNG) defence personnel, were on the ground, but heavy equipment required for the rescue had yet to reach the remote village, as the main road remained cut off and the only access was via helicopter.

PNG government authorities remained focused on clearing debris and improving access to the village, the UN said in its latest update. The agency was preparing to move and distribute food and water, and said it was helping set up evacuation centres.

Social media footage posted by villagers and local media teams showed people scaling rocks, digging with shovels, sticks and their bare hands to find survivors. Women could be heard weeping in the background.

Six bodies have been retrieved so far. The UN said the number of possible deaths could change as rescue efforts were expected to continue for days.

PNG media on Monday reported that residents had rescued a couple trapped under the rubble after hearing their cries for help.

Johnson and Jacklyn Yandam told local NBC News that they were very grateful and described their rescue as a miracle.

"We thank God for saving our lives at that moment. We were certain that we were going to die but the big rocks didn't crush us," Jacklyn said. "It's really hard to explain as we got trapped for nearly eight hours, then got rescued. We believe we were saved for a purpose."

Dangerous conditions

The UN migration agency said that water continued to flow under the debris, making it extremely dangerous for residents and the rescue team to clear it.

Serhan Aktoprak, the chief of the UN migration agency's mission in PNG, told ABC television that emergency crews would continue to look for survivors until the residents asked them to stop.

Aktoprak said that the rescue team had eight vehicles but that he hoped to receive additional resources soon. About 1,250 people have been displaced by the landslide, which occurred in PNG's Enga province early Friday.

More than 150 houses were buried and about 250 houses were abandoned.

"The houses are buried under around eight metres (26.3 ft) of dirt. So there is quite a lot of debris to get through," aid group CARE International PNG country director Justine McMahon told ABC television on Monday. About 4,000 people were living near the affected area, she said.

Neighbours Australia and France, which rules the Pacific island of nearby New Caledonia, have said they stand ready to assist PNG.