Authorities are investigating another suspected case of H5 bird flu after five giant petrels were found on a beach near Esperance on Western Australia’s southern coastline.

It is the fifth case being investigated after two migratory birds found in WA and one in South Australia tested positive to the highly contagious virus.

Agriculture Minister Jackie Jarvis told media a member of the public reported five giant petrels at Roses Beach on Sunday.

“Only one of the petrels has returned a suspected positive result for bird flu,” she said.

“The other four birds returned negative results.”

A giant petrel found in Quindalup, in WA’s South West, on Saturday is still being investigated.

The CSIRO will test samples from the suspected cases to determine if they are positive.

Ms Jarvis said there were still no signs of mass mortalities, or detections in poultry or wildlife.

“There is no evidence of disease transmission here on the Australian mainland,” she said.

South Australia confirmed its first case of avian influenza on Wednesday, with one bird testing positive.

The migratory seabird, a giant petrel, was found at Knights Beach on the Fleurieu Peninsula on June 14 next to another petrel, which tested negative.

WA has two confirmed cases of H5 bird blue, that were found in Esperance last week.

A sick brown skua was found on a beach and taken to a wildlife hospital on June 14, another giant petrel was found four days later.