The majority of the 78,000 islanders had left their homes after hearing of an imminent earthquake even bigger than the 8.7-strong one that pounded the area on Monday, Simeulue district chief Darmili told AFP.

Continuing aftershocks intensified the panic on the island, which had only just begun picking itself up after the 9.3-strong December earthquake that unleashed a tsunami that killed around 273,000 people across the Indian Ocean.

Knowledge passed down through the generations about the signs of a looming tsunami had helped tiny Simuelue escape major fatalities in December: when villagers saw the sea recede, they fled to higher ground.

Now most are too afraid to return.

"What is certain is that now a majority of the population of Simeulue are now refugees," said Darmili, who only uses one name.

"The people are now in great fear and are worried because there is a rumour circulating that an even more massive earthquake will soon occur again," he said.

An emergency assessment of remote areas of the island that could only be accessed by motorbike revealed Monday's quake had caused more damage than initially believed, UN aid operations coordinator Michele Lipner told AFP.

"In some areas we have 70-80 percent structural damage and in some villages, up to 100 percent," Lipner said.

The death toll remained at 17, substantially lower than the some 1,000 estimated to have died on neighbouring Nias island, with nearly 180 people injured, she said.

The December quake killed only seven people on Simeulue and damaged around a third of the island's 15,000 homes, along with the hospital and mosques, local officials said at the time.

The UN said it had assessed half of the island by late Thursday, finding that nearly 40 percent of the islanders had left their homes in fear of another disaster.