Boulders "the size of cars" roared down the crowded slopes of Malaysia's Mount Kinabalu after its earthquake, a witness said, as authorities on Sunday raised the death toll in the disaster to 16.

Six Singapore primary school students and a teacher who were on an excursion to the peak were among those killed when the 6.0-magnitude quake struck Friday morning, sending landslides crashing downward.

Authorities said two more people remained missing on the mountain.

The earthquake hit just as the 4,095-metre-high (13,435-foot) mountain, a popular destination for hikers, was crowded with visitors seeking its sunrise views over Borneo island.

"I saw large rocks, like the size of cars... falling all around us. I also saw landslides around the summit area," said Mohammad Razif Hadzri, 30, a Malaysian university employee.

Miraculously, none in his party of seven were hurt.

"We were lucky the large stones didn't fall on us, but around us. It was quite scary," said Razif.

Local mountain guides who accompany climbers helped them find the painstaking way down through the devastated trails, a trip that took 17 hours. It normally takes three to four hours.

Singapore Foreign Minister K. Shanmugam confirmed that the bodies of six students had been identified.

Another teacher and an adventure guide from Singapore also perished, while a student and a teacher remained missing, Shanmugam said.

Malaysian officials have said the students were aged 12 and 13.

"Looking at the photos of these children -- such young lives, full of promise, snuffed out," Shanmugam said in a Facebook posting.

Singapore declared Monday a day of national remembrance for the victims.

Malaysian police say the dead or missing also include several Malaysians, and one each believed to be from China, Japan and the Philippines.

But they were yet to provide a detailed breakdown, saying the poor state of some remains made identification difficult.

Body parts had been found on sections of the mountain, suggesting the awesome power of the landslides, police added.

Singapore's Straits Times newspaper said some of the students were taking a route to the summit known as the Via ferrata, Italian for "iron road", that traverses a steeply sloping granite rock face.

"Initial investigations show that the worst-hit area was at Via ferrata. There were many boulders that came down there," Masidi Manjun, tourism minister of the Malaysian state of Sabah where the mountain is located, told reporters.

- Climber criticises rescue effort -

Rescuers Saturday had escorted down to safety 137 hikers who were stuck on the mountain for up to 18 hours by the rockfalls.

But an Australian climber accused Malaysian authorities of a slow and chaotic response.

"The whole government emergency response was a farce," Vee Jin Dumlao told the Australian Broadcasting Corporation, asking why stranded hikers were not reached by helicopter.

Officials have said poor visibility at the summit made a helicopter mission dangerous.

Masidi said on Twitter that the search and rescue effort would be examined afterward but added, "Now is not the time to blame."

Dozens of aftershocks have followed the main quake, the strongest being a 4.5-magnitude temblor on Saturday afternoon.

Friday's quake was one of Malaysia's strongest in decades but there have not been any reports of major damage, nor any casualties outside of those at Mount Kinabalu.

The mountain has been closed for at least three weeks so authorities can repair trails and facilities and assess safety risks.

Around 20,000 people complete the relatively easy climb each year.

Some officials and social media users have blamed the quake on a group of 10 apparently Western tourists who last weekend snapped nude photos at the summit and posted them on the Internet, saying the act angered local tribal spirits.

Mount Kinabalu is sacred to Sabah's Kadazan Dusun tribe.

Masidi said two Canadians had been detained over the photo incident but declined to identify them or say what charges they may face.