The walls were swaying as Tori Taylor tried to feel her way across them in the dark after the 6.9-magnitude earthquake shook the island of Gili Trawangan, off Lombok in Indonesia, last Sunday.

There had been another large tremor the week before, but this one felt larger.

“It was unbelievable, crashing sounds, rumblings of the earth, falling tiles, smashing glass, spraying water, people screaming – absolutely terrifying,” the American, who runs a dive resort, wrote in a diary she has kept of the disaster.

On nearby Gili Meno, Andi Darmin huddled on the roof of his bungalow with his guests, including a couple and their eight-month-old baby. “Can you get a helicopter?” one of the European guests asked him. “I will pay whatever it costs.”

The earthquake, which centred on northern Lombok, left at least 321 people dead, 1,033 seriously injured and 270,000 people displaced from their homes. Indonesia’s disaster and rescue agencies expect the death toll to rise further. Satellite imagery shows that in North Lombok 75% of settlements were destroyed.

Play Video 0:34 Amateur footage appears to capture moment of Lombok earthquake – video

Although they escaped the worst of the disaster, the Gilis – three idyllic islands popular with divers, party lovers and honeymooners – were plunged into emergency mode.

On Gili Air, a western doctor and a few English nurses on holiday banded together to erect a makeshift medical tent in a field to treat the wounded, and instructed expats to collect painkillers and other supplies from tourists.

On Gili Trawangan, the biggest of the three islands, where at least eight people died, doctors, dive instructors and tourists set up a basic camp with oxygen and medical supplies and organised people into groups from minor injuries to the most severe.

The bodies of the dead were laid out on the beach on sarongs before they were taken away to be cleaned for burial. Many people camped out overnight, too afraid to sleep indoors.

Facebook Twitter Pinterest Devastated buildings on the Gili islands. Photograph: Kate Howard

Thousands of panicked tourists left the islands the following day, in some cases scrambling over each other to get a seat on one of the boats. Most headed straight for the international airport, where some slept on the floor as they waited for a flight out.

The exodus leaves the mostly western-run tourist businesses facing an uncertain future.

“When I look to the right there is no one, when I look to the left there is no one, just hundreds of bikes dumped at the port,” said Sander Buis, the Dutch owner of Oceans 5 Dive on Gili Air.

He estimated that about 70% of resorts on Air had been damaged, and many homes owned by Indonesians in the centre of the island destroyed.

“The weirdest part is that it is not just one part that is totally damaged. Some resorts are not in good shape. Others have no damage at all.”

Facebook Twitter Pinterest Abandoned bicycles on Gili Trawangan. Photograph: Ulet Ifansasti/Getty Images

On Gili Trawangan about 30% of buildings have been destroyed and another 40% damaged. Authorities estimate that the cost of the damage across the Gilis and Lombok could easily exceed 1tn rupiah (£53m).

On Friday there was no running water on Gili Trawangan or Air, though there were plenty of supplies – in contrast to the more serious situation on the worse-hit main island of Lombok. Before electricity was reconnected, the owners on Air were clearing out all the island’s fridges and giving away the meat to local residents, who are sending it to their families in the north.

Horses used to pull carts on the car-free island of Trawangan were being rounded up after running loose, and taken to the mainland. After reports of looting on Trawangan – there are no police on the Gili islands and it took days for the military to arrive – the security situation was improving.

Facebook Twitter Pinterest A man guides a horse onto a boat to transport it to the mainland from Gili Trawangan. Photograph: Antara Foto/Reuters

As aftershocks continue – there had been more than 450 by Friday – tourists are likely to stay clear of Lombok and the Gilis for now.

Buis said he hoped things would start to feel more normal within six weeks. “Some resorts are not that damaged at all and some are,” he said. “So it is all about when the tourists are ready to come back.”