Hundreds of dead starfish have washed ashore on Perth’s southern beaches with tests underway to try to determine what killed them.

The Department of Fisheries (DoF) was alerted on Monday that up to 1000 starfish had been found on South Beach and in North Coogee.

About 200 starfish were found by fisheries officers who checked the beaches on Monday and Tuesday, however no other dead sea life was discovered.

Samples collected by the officers have been sent for analysis.

The cause of death remains unknown and results from the tests could take some time, the DoF said.

Fisheries officers will continue to monitor the beaches in the meantime.

Thousands of dead fish washed up in Cockburn Sound south of Perth in November last year.

A toxic algal bloom was later identified as the likely cause of death.

The latest find has prompted a warning for people to avoid swimming or fishing in areas with large numbers of dead or decomposing fish.

Meanwhile the DoF said the public’s help in reporting fish kills was important because it allowed them to respond quickly and take samples.

-ABC