Sydney  - The Twelve Apostles rock formations on Australia's south coast that thousands of tourists photograph each year as they drive along the Great Ocean Road now number just seven after one more limestone stack collapsed into the sea.

"It will always be the Twelve Apostles," Parks Victoria spokeswoman Jo Curkpatrick told national broadcaster ABC on Saturday when confirming the loss. "It remains unique, no matter how many Apostles come and go."

Previous recent losses to erosion occurred in June, and in 2005. Geologists say it is likely all will eventually disappear.

Fifteen years ago one of the biggest stacks collapsed, leaving a couple stranded on an island. They were picked up by helicopter.

The Great Ocean Road runs part of the way between Melbourne and Adelaide.

A stop at the Twelve Apostles is a highlight of a 300-kilometre scenic route that begins 100 kilometres west of Melbourne and runs through Port Campbell to Warrnambool. (dpa)