Officials are still trying to pinpoint how many people are buried under parts of a mountain which collapsed onto the Yambali village in the Enga region a week ago.
More than 2000 people might have been buried alive, according to the PNG government.
PNG officials have shifted from a rescue to a recovery mission at the remote site. (Supplied by Iom Papua New Guinea/AAP PHOTOS)
A UN estimate put the death toll about 670.
Marape apologised to residents for not visiting earlier, The Papua New Guinea Post Courier reported.
"I'm sorry," Marape was cited as saying.
"The country is with you in your time of sorrow."
He has pledged 20 million kina ($A7.8 million) for emergency response and initial recovery measures.
Marape also inspected the disaster site by helicopter, the United Nations migration agency said.
Heavy equipment and aid have been slow to arrive because of treacherous terrain and tribal unrest in the area.
As of Thursday, PNG government officials had ruled out finding survivors under the rubble and said they would shift focus on recovering bodies.
The UN migration agency said the disaster site will be quarantined by PNG authorities after 14 days and access will be restricted in a bid to prevent the spread of diseases decaying bodies.
The United Nations has said water flowing under the debris had contaminated the village's water sources.
Those who remain undiscovered would be declared missing, the agency said.
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