A man views a house that collapsed in a strong earthquake in Halagoli, Hela Province, Papua New Guinea. File picture: Jerol Wepii via AP

Sydney - The death toll in Papua New Guinea following last week's devastating magnitude-7.5 earthquake has risen to at least 75, authorities said Tuesday.

The earthquake severed the communication and transport networks of the remote provinces of Southern Highlands, Hela, Enga and Western, some 560 kilometres north-west of the capital Port Moresby.

The country's disaster management authorities said the number of dead is 75, while provincial officials report more than 100 fatalities. The tremor was one of the strongest in the region in recent years. 

Papua New Guinean Prime Minister Peter O'Neill called it "an unprecedented disaster" and declared a state of emergency in the quake-hit areas.

Read: Quake kills 14 in Papua New Guinea; ExxonMobil plant shut

There have been sustained aftershocks, including a magnitude-6.0 quake on Monday.

"Some 143 000 people have been affected. At least 17 000 people or more than 3 000 households have become internally displaced," Udaya Regmi, the head of the International Federation of Red Cross and Red Crescent Societies in the country told dpa from Port Moresby.

Regmi said more than 500 people have been injured and many have not been able to get access to healthcare because the quake has damaged local hospitals.

"So the delivery of much-needed relief has been badly hampered," Regmi said. "We don't know of any relief organization who has been able to reach a few of the hardest-hit areas."