(CNN) More than 140 short-finned pilot whales died after a mass stranding on a beach in Western Australia on Friday.

A group of around 150 whales became stranded at Hamelin Bay, around 300 kilometers south of the state's capital city Perth.

Six surviving whales had been returned to the sea as of 7.00 p.m local time (7.00 a.m. ET), Western Australia's Parks and Wildlife Service said.

"Unfortunately, most of the whales beached themselves on dry land overnight and have not survived," Incident Controller Jeremy Chick said.

Chick said moving the whales by nightfall was logistically challenging because of the rocky beach terrain and rough seas.