Australia baffled as unidentified mystery object washes up on beach

Police have been baffled by a mysterious "unidentified" dome that washed up on a West Australian beach.

The giant metal object was found by locals at Green Head beach, about 250kms north of Perth.

State and federal authorities are investigating the item, which is not currently believed to be from a commercial aircraft.

It is being treated as hazardous, and police have requested people keep a safe distance.

"We want to reassure the community that we are actively engaged in a collaborative effort with various State and Federal agencies to determine the object's origin and nature", police said in a statement.

Green Head beach residents said the cylinder was about 2.5m wide and between 2.5m and 3m long, Australia's public broadcaster reported.

Residents visited the site on Saturday night to see the cylinder, the ABC reported, with one local describing it as a "great social evening".

"It was a lovely, still night, the kids were digging sand castles around it," he told the ABC.

Aviation expert Geoffrey Thomas said the item was possibly a fuel tank from a rocket that had fallen into the Indian Ocean at some stage in the past twelve months.

While there was some speculation the cylinder may have been a part of MH370 - a plane that went missing off the west Australian coast in 2014 with 239 passengers on board - Mr Thomas said there was "no chance".

"It's not any part of a Boeing 777 and the fact is MH370 was lost nine and a half years ago so it would show a great deal more wear and tear on the debris," he said.