Thousands of tourists are trying to get off Indonesia's Gili Islands in the wake of a magnitude-6.9 earthquake which collapsed buildings.

One of them is Sebastiaan Evans, a British trader, who described his ordeal to the ABC as he waited for the Indonesian Navy to arrive.

Loading

He said the quake hit the islands just after 7:30pm (local time).

"Our swimming pool was shaking so much water was overflowing into our bedroom," he said.

"We went to the reception of our hotel but they weren't telling us what we should do.

"So we went to the streets to see if any of the locals could give us more insight and they told us to run to the hills as fast as possible because there was a tsunami on its way."

Mr Evans said as he tried to get to the hills as fast as he could, he heard the waves "crashing against the beach".

"People were screaming and shouting that a tsunami was coming," he said.

"There were thousands of people on that hill, waiting for more information.

"There were aftershocks, which caused people to scream and shout."

He said he had to stay on the hill until 6:00am the next day.

Tourists wait to board the boats. ( Supplied: Sebastiaan Evans )

"Throughout the entire process, there's been no official information, it's all been what you hear from the locals," he said.

"We then found out this morning that Gili T [Trawangan], Gili Meno and Gili Air were being evacuated by the Navy. So we had to get on a boat."

Sorry, this video has expired Tourists swim after boat evacuating Gili Air

Mr Evans said he was still waiting on the beach to board one of the boats.

"We just witnessed one of the boats get completely overfilled with tourists climbing on, with the officials trying to keep them back off the boat, pushing them and shoving them. That boat still hasn't left yet," he said.

"I've just been to two first-aid sections, one has got people who are still alive, the other one has got a few dead bodies in it."

Roofs collapsed on buildings on the Gili Islands. ( Supplied: Sebastiaan Evans )

Mr Evans said he had heard there was a call-to-prayer during the earthquake and that a local mosque had fallen down, causing "serious damage".

"People died in that collapse, we've been told," he said.

Houses were damaged on the Gili Islands. ( Supplied: Sebastiaan Evans )

"A lot of the main structures had fallen down and allegedly 14 people have been killed in that.

"There were more bodies loaded onto boats earlier."

Mr Evans later told the ABC he had given up waiting for a ferry and had joined others in camping on the hill and sleeping rough for a second night.