Video: Slacklining Daredevils In 330ft Stunt

Balanced 328ft above an Australian valley, two daredevils have been showing off the latest extreme sport to enter the mainstream - slacklining.

German tourists Florian Herla and Niklas Winter were filmed walking across the 115ft-long thin strip of nylon at Hanging Rock, in Central Victoria.

Hundreds of millions of Super Bowl viewers watched Andy Lewis' acrobatic routine on a slackline during Madonna's halftime show at the weekend, boosting the sport's mainstream audience.

As its name suggests, slacklining is similar to tightrope-walking but involves the use of a flexible line instead of a taut rope.

Its origins can be traced back to the US in the 1980s, but it has grown hugely in popularity over recent years and has developed into various forms.

A National Parks and Wildlife spokeswoman said the stunt at Hanging Rock on Sunday appeared to be illegal.

"It's illegal without prior approval from the park manager if it's a risky activity, which this clearly is," she said.