More than 140 whales are dead after a mass stranding at Hamelin Bay, 315 kilometres south of Perth, sparked a shark advice alert for the area and a major rescue operation.

About 150 whales were spotted on the beach by a fisherman about 6:00am on Friday after washing up about one kilometre north of the boat ramp at the beach, 10 kilometres north of Augusta.

Almost all of the mammals — short-finned pilot whales weighing between 1-4 tonnes — have now died, with six survivors helped back out to sea late in the afternoon.

Authorities used large cranes with slings to transport the whales about 1 kilometre down the beach.

People cheers, clapped and hugged as the surviving whales swam out to sea.

Volunteers — many of them just regular beachgoers who wanted to help — swam into the water with the mammals to try to encourage them back into the water.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 22 seconds 22 s Dozens of whales stranded at Hamelin Bay

One whale got caught on rocks as it tried to swim back to shore, but wetsuit-clad rescuers plunged into the cold water to push it to safety.

Shannon Stent was one of the volunteers who worked to try to save the whales.

"Most of us have been there all day," he said.

"We're focussing on the positives … we're doing all we can."

The vast majority of the stranded whales could not be saved. ( Supplied: Leaarne Hollowood )

Speaking earlier, Department of Biodiversity, Conservation and Attractions (DBCA) incident controller Jeremy Chick said the welfare of the surviving whales was the priority.

"Unfortunately, most of the whales beached themselves on dry land overnight and have not survived," he said earlier.

"There are only [a few] surviving in shallow waters.

"Rescue operations will be hampered by deteriorating, weather conditions and we need to ensure the safety of everyone involved."

Rescuers work to save a group of 150 stranded whales at Hamelin Bay. ( ABC News: Megan Morris )

Visitor service coordinator Ben Tannock said people were being asked to keep well clear of the animals.

An incident management team including veterinarians spent the day on site.

"We're obviously managing the animals and the palliative care of those animals, and the rescue of the animals that are still alive, if possible," Mr Tannock said.

One of about 150 pilot whales that have beached themselves at Hamelin Bay near Augusta. ( Supplied: Department of Biodiversity, Conservation and Attractions )

Race against time before ex-cyclone approaches

Mr Tannock said while their efforts were focused on the whales, it was also a big job to manage the public who had gathered at the scene.

"Obviously in these certain incidents there's high requirement to manage the public interaction as well," he said.

"It becomes quite an emotive issue and the public will themselves want to get involved.

"It is certainly terrific to have them on site, but they need to work under the guidance of Parks and Wildlife Services staff and make sure the incident is controlled and managed properly."

It is estimated more than 150 whales have stranded themselves at Hamelin Bay, near Augusta. ( Supplied: Leaarne Hollowood )

Hamelin Beach is closed from Hamelin Caravan Park to North Point including Grace Road and Reserve Road.

The Bureau of Meteorology is expecting a swell to start rising in the South West from Sunday as a result of Tropical Cyclone Marcus.

DBCA said that could make the rescue effort a race against the clock.

Surfers who had been looking forward to the super swell have also been warned by the Fisheries Department the whales are expected to attract sharks.

The whales beached themselves about 300 kilometres south of Perth. ( Supplied: Department of Biodiversity, Conservation and Attractions )

"It is possible the dead and dying animals will act as an attractant, which could lead to sharks coming close in to shore along this stretch of coast," the alert said

"While it's not uncommon for sharks to be present off the Western Australian coast throughout the year, people should exercise additional caution until the stranding incident is resolved."

Surf Life Saving WA have tweeted that a three-metre shark of unknown species has been spotted in the area.

Big job to remove dozens of carcasses

The DBCA is working with the Shire of Augusta-Margaret River to remove the dead whales from the beach.

DNA samples are being taken from the deceased whales to try to determine why the whales became stranded.

It will be the local shire's responsibility to dispose of the whale carcasses, which are already creating a powerful smell.

Dead whales lie on the beach at Hamelin Bay after a mass stranding. ( ABC News: Megan Morris )

DBCA wildlife officer Pia Courtis said the team was waiting on an excavator to arrive at the beach to be able to save the whales which are still alive.

Dozens of volunteers and wildlife officers will remain there overnight, or for as long as it takes to move the whales to the boat ramp and safely push them back out to sea.

"The plan is to get the excavator down here and move the live ones to an area closer to the boat ramp," Ms Courtis said. "Hopefully we'll refloat them and send them back out as a group."

Rescuers work to save stranded whales at Hamelin Bay. ( ABC News: Megan Morris )

She said they had no indication of when that might be.

"At the moment we've got officers and volunteers down there and they're stabilising the whales," she said.

"Of course for us our biggest concern is them being out of the water and sunburn. So we've got them covered and we're trying to keep them as moist as we can."

Rescuers at Hamelin Bay splash water on a beached whale to try to keep it alive. ( ABC News: Megan Morris )

Rescuers left distressed

UK visitor Barrie Brickle said the scene on the beach earlier on Friday was distressing, as the whales repeatedly beached themselves after being pushed back to sea

"[Volunteers] seem to drag them up onto the beach, get them the right way up and then they seem to revive," he said.

"But the ones I've seen that are back in the water, they actually come back around and beach themselves again.

"I watched one of them - it happened three times but still it wouldn't go back to sea."

Rescuers try to re-float a stranded whale at Hamelin Bay. ( ABC News: Megan Morris )

At least half the whales have already died. ( Supplied: Department of Biodiversity, Conservation and Attractions )

Scene of previous strandings

In 2009, more than 80 pilot whales and dolphins died in a mass stranding at Hamelin Bay on the same day — March 23. More than 20 whales were also stranded in the South West town of Bunbury in 2015.

The biggest mass stranding of whales in WA was in Dunsborough in 1996, when 320 long-finned pilot whales beached themselves.

"The South West capes area has had a number of incidents over the years of stranding of short fin and long fin pilot whales, so they're a species that are common in terms of a stranding scenario," Mr Tannock said.

Short-finned pilot whales can grow to up to 5.5 metres long and are occasionally seen in groups as large as several hundred, but more commonly travel in groups of less than 100.

They are brownish-grey to black with a pinkish-grey anchor shape on the undersides, and inhabit tropical and sub-tropical waters, according to DBCA.

Hamelin Bay, Western Australia. ( ABC News: Sharon Kennedy )

Shark warning for swimmers

Authorities are warning people to:

Take additional caution in the Hamelin Bay area

Take additional caution in the Hamelin Bay area Adhere to beach closures advised by Local Government Rangers or Surf Life Saving WA.

Adhere to beach closures advised by Local Government Rangers or Surf Life Saving WA. Keep informed of the latest detection and sighting information by checking the SharkSmart website or Surf Life Saving WA's Twitter feed.

Keep informed of the latest detection and sighting information by checking the SharkSmart website or Surf Life Saving WA's Twitter feed. Report shark sightings to Water Police on 9442 8600.