Testing is still under way on a second bird after Australia's first case of the deadly H5 bird flu was confirmed on WA's south coast.

Agriculture Minister Julie Collins announced on Friday a bird has died and the initial test was positive for H5N1. Further tests will be performed for confirmation.

The deadly H5N1 strain of bird flu is suspected to have reached mainland Australia for the first time.

The first case of H5 bird flu in mainland Australia has been confirmed.