The suit-clad men were drinking at the Vue de Monde restaurant Tuesday on level 55 of the 56-floor building before slipping past security measures and jumping off the balcony, the Melbourne Herald Sun reported Wednesday.
"Basically, four guys came upstairs with parachutes hidden underneath their jackets," restaurant owner Shannon Bennett told the newspaper. "They ordered some drinks at the bar. One went to the bathroom, followed by the rest, straight out to the balcony and pretty much jumped straight off."
Bennett said it appeared as though the men were wearing helmets with cameras attached, so he hopes to find a video of the jump on YouTube to help track down the culprits. BASE jumps are a common occurrence at the Rialto Towers, the Herald Sun reported, and Bennett said he thinks the men must have researched the restaurant's security measures ahead of time.
"It was just too late, they were just really quick at what they were doing, it was just very well planned and they've obviously done this sort of stuff before," he said.
BASE stands for four categories of fixed objects from which one can jump: buildings, aerials, spans (bridges) and earth (cliffs).