Twelve whales died on Monday after stranding themselves against a rocky breakwater on Australia's west coast, with experts working hard to save another four.

The pod of long-finned pilot whales got into trouble in Bunbury harbour, 175 kilometres (110 miles) south of Perth, Western Australia's Department of Parks and Wildlife said.

The department's nature conservation leader Kim Williams said 12 whales had died, and six had been herded out to sea by small boats.

"This afternoon's efforts have focussed on the rescue of four remaining whales that were stranded in the shallows, and they were pulled out to sea using a sling and boats," he said in a statement.

"Unfortunately one of these whales has re-stranded and is being taken out to deeper water again, while the other three are not swimming strongly and there is a chance they will also re-strand."

Williams said it was hoped that the released whales would join another pod of 15 long-finned pilot whales which has been swimming in the area all day.

Whale beachings are relatively common in Australia, but scientists do not know why they happen.

In 2009 a group of long-finned pilot whales, which can grow up to 6.5 metres (21 feet) in length, stranded themselves in Hamelin Bay, south of Bunbury, with efforts to save most of them failing.