Like any musical group, Danish quintet Aquasonic sing and play instruments - such as Tibetan bells, violin and organ - but they do it while submerged in tanks filled with water.

The group started in 2004 when composer Laila Skovmand put a bowl of water to her lips in her kitchen and began to sing into the water's surface. Gradually, she experimented with different sounds, reported Huffington Post.

Since then, Ms Skovman, along with co-founder Robert Karlsson, have taken their unique genre of music around the world to festivals such as this year's Sydney Festival, which starts today.

Aquasonic's repertoire includes mermaid songs and even white noise, which is amplified via hydrophones and loudspeakers.

No oxygen tanks needed - the musicians come up to breathe at specific intervals that are incorporated into each composition. These intervals are also unique to each musician, depending on how physical his role is.

Mr Karlsson said: "Thirty seconds (underwater) can be a long time, especially for the drummers. They are physically very active because you need to use so much force in the water."