(CNN) The death toll from a magnitude-7.5 earthquake that hit Papua New Guinea's remote highlands last week has risen to 67, the Red Cross said.

Massive aftershocks continued to rattle the region.

The February 26 quake struck near Porgera in the Pacific nation's Enga province, destroying houses, causing landslides and damaging a major gas plant.

"The national disaster center estimates that 67 people have died and 500 are wounded," said Udaya Remi, the head of the Red Cross in Papua New Guinea.

"It's very difficult to get accurate information because of damage to roads and the remoteness and ruggedness of the area, but it's thought that 143,000 people have been affected and 17,000 displaced."

The latest aftershocks, which included a magnitude 6 quake, struck on Monday in the same area, about 600 km (370 miles) northwest of the capital Port Moresby, according to the US Geological Survey.

Prime Minister Peter O'Neill has declared a state of emergency in the affected areas.

The region is largely rural with no major urban centers, but around 670,000 people live within 100 km (62 miles) of the quake's epicenter, according to the Red Cross.

Damage to a road near Mendi in Papua New Guinea's highlands region on February 27.

The Red Cross, Australia and New Zealand have pledged aid, but the remote area has proven tough to access owing to the combination of rough terrain, bad weather and damaged transport and communications infrastructure.

"People are finding it difficult to get to hospitals and health centers because of landslides and long distances," said Remi.

"We have people in the field who are assessing the situation. We'll then decide what sort of operation is needed in terms of food security, health and sanitation."

Southern Highlands Acting Provincial Administrator Thomas Elluh said the people in his province are in dire need of relief supplies, especially food, water and shelter, Papua New Guinea Today , an online news website, reported.

Debris from a massive landslide from Monday's earthquake covers an area in Tabubil township.

According to the website, Elluh called on the government to speed up efforts to assist the affected areas.

"The rugged terrain and loss of communications in the area impacted means it is taking time to build a complete picture of the damage but we know that tens of thousands of people are reported as requiring humanitarian assistance," New Zealand Foreign Affairs Minister Winston Peters said in a statement on Monday.

US energy giant ExxonMobil announced that it would take about eight weeks to restore production at the Papua New Guinea liquefied natural gas project (LNG), which was damaged in the quake.

"We have assembled a team of technical experts from ExxonMobil's global workforce to help the local team complete damage evaluations and restore production," said ExxonMobil Papua New Guinea managing director Andrew Barry in a statement.

"It is very important that we recover as quickly as possible to restore normalcy for our workforce, help our nearby communities to recover and contribute important revenue for the country."