(CNN) Tourists in Iceland were left fleeing to higher ground on Sunday as a large wave triggered by a glacier collapse came rushing their way.

Stephan Mantler, a mountain guide and owner of Icelandic tour company Hafjall, captured the whole ordeal on camera. Tourists were admiring the Breiðamerkurjökull glacier in Vatnajökull National Park in southeastern Iceland. This area is only accessible with a trained mountaineer, according to Mantler.

Mantler said he could hear the cracking from the far-off glacier, which is a sign that a glacier calving -- the natural process in which a large section of ice breaks away -- was imminent. With his client safe, he pulled out his phone and started recording, but kept his eye on the other group of tourists below.

"I could see all of them start to move out of harm's way and their guides also ready to jump into action if necessary, so I kept recording but with a watchful eye on people's movements," Mantler said.

In the video, you can hear rumbling that sounds like thunder as the pieces of the glacier crash into the water below. People start running to higher ground as waves approach them.

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