Thousands of starfish have washed up on Moreton Island off south-east Queensland in a mass stranding spanning kilometres.

Tour guide Rhett Ericsen-Miller filmed the starfish at the Ben-Ewa campsite, describing the spectacle "tragic yet beautiful".

Stunned tourists walking the beach feared it was "mass suicide" but University of Queensland marine biologist Kathy Townsend said it was a natural phenomenon.

Dr Townsend said a combination of a strong north-westerly and rough weather aligned to cause the animals to lose their grip on the seagrass beds in which they live.

The starfish, also known as sea stars, did not appear to have wasting disease or lesions.

"It is due to a change in the wind, weather, and tides," she said.

"All the conditions were in line for that event to occur."

Dr Townsend said the strandings usually happened once a year, but it is the second one in several weeks.

The population was still healthy, Dr Townsend said, despite the huge number of deaths.

"Just two days ago I was out there and there is still a lot," she said.

"It doesn't appear to have affected the population overall."

She recommended tourists throw the animals back into the sea to give them a chance at survival.

"They can survive a certain amount of dehydration," she said.

Speculation starfish have come together for breeding

School of Biological Sciences Adjunct Professor John Lucas said it was the time of year for starfish to breed.

"It is common for marine animals that shed their eggs and sperm into the water to aggregate to improve fertilisation rates," he said.

"There has obviously been mass mortality in a dense population."

The video of the stranding was posted on Facebook, acquiring more than 32,00 views since Monday.

Mr Ericsen-Miller's colleague Terry Howard said the starfish spread in batches for about 10 kilometres across the Island, off Brisbane, from Ben-Ewa to Tangalooma Point.

He was not overwhelmed by the sight.

He sees it every year.

"The tourists are surprised by it but they accept that it's part of what you see on the island."