The northern part of Queensland state in Australia could be in for a possible tsunami threat after a group of researchers discovered a collapsing sea floor at the Great Barrier Reef.

Marine geologists from Australia's James Cook University said the Noggin Block, a one-cubic-kilometre slab, remnants of an underwater landslide that currently sits suspended on the continental shelf's edge, could break away anytime.

"It's actually up on the top of the continental slope in about 350 metres of water," geologist Robin Beaman said.

"This block . . . is in the very slow, early stages of starting to break away from the edge of the Great Barrier Reef."

And if it does break away, "it will break away really quickly . . . it would actually cause a tsunami." The marine biologist noted a catastrophic event, such as an earthquake that measures more than seven on the Richter scale, would potentially trigger the occurrence.

The tsunami threat, Mr Beaman said, would travel across the Great Barrier Reef, about 70 kilometres offshore, and would definitely impact the local North Queensland area.

Situated about 100km southeast of Cairns, the block is between 340 metres to 470 metres deep. Age-date testing conducted on the deep water corals breeding on the block revealed it is a thousand years old.

Mr Beaman said they cannot give any specifics as to when the collapse will occur. "Whether tomorrow or even in our lifetime, but people should be aware that it was there."

"It is slowly giving way although it remains stable under current conditions," he said.

"But it is absolutely going to collapse and when it does fall it will fall one kilometre into the adjacent basin."

Should it happen, the tsunami would take an hour to hit coastal areas such as Mourilyan Harbour and Clump Point, south of Cairns.