Three mass bird mortalities involving more than 1000 crested terns have been reported amid a distressing spread of avian influenza.

South Australian authorities said on Thursday the coastal birds were discovered on Wednesday and were believed to have died from H5N1.

Premier Peter Malinauskas told SA Parliament the deaths occurred on remote offshore islands, the ABC reports.

The islands included Troubridge Island off Yorke Peninsula and two small islands off Kangaroo Island known as North Page and South Page.

Another case of a dead little penguin from Kangaroo Island was also under investigation.

As of Wednesday there were 236 confirmed H5 bird flu events in wild birds, with most in South Australia.

Authorities have received more than 21,000 calls to the Emergency Animal Disease Hotline since the outbreak began.

Tasmania’s tally has jumped to 10 after four more wild birds on King Island tested positive, with two crested terns and two silver gulls found dead on beaches and bays around Currie.

Authorities say the focus remains on early detection and surveillance, with crews inspecting about 760 kilometres of the state’s north-west coastline and no mass die-offs reported.

In Western Australia, wildlife experts warn the virus is already creating an animal-welfare crunch as some private veterinary clinics stop accepting birds and, in some cases, other wildlife altogether.

Meanwhile, hundreds of young pelicans have been found dead at Lake Cawndilla in outback NSW.

However, samples have ruled out bird flu as the cause of death.

Further testing is underway but authorities say it may take weeks to determine what happened to the 400 pelicans.

-with AAP