A Filipino geothermal energy company has described the loss of four of its employees, including two Australians working as consultants, as an "unthinkable tragedy".

Simon Chipperfield and Karthi Santhanam were killed when a Cessna 340 crashed on Saturday morning.

Also killed were pilots Rufino James Crisostomo and Joel Martin.

"Tragically, there were no survivors. My heart goes out and my condolences go to the families of two Adelaide men who were on that flight," Mr Albanese told reporters in Adelaide on Thursday.

"My condolences also to the people of the Philippines for the Filipino nationals who have lost their lives in this tragedy."

He said Department of Foreign Affairs and Trade officials were providing assistance to the families of the two Australians.

"They are in direct contact, and the families' wishes will be respected," Mr Albanese said.

The men were working with the Energy Development Corporation, which said it stood "in compassion and deep sorrow with the families of our fallen Kapamilyas in this unthinkable tragedy".

"We are working with authorities to bring them home to their loved ones where they may rest in peace," the company said.

"Our heartfelt sympathies go to their families and friends at this difficult time."

The plane came down near one of the country's most active volcanoes shortly after taking off from Bicol International Airport in the Alby region for the hour-long flight to Manila.

The victims were brought down from the site on Thursday after a search involving almost 200 troops, firefighters and volunteers, including veteran mountaineers, that was hampered by heavy rains, gusty wind and thick clouds.

The wreckage was spotted from the air on Sunday on the slopes of the 2462-metre volcano, but an air force helicopter only managed to ferry the search team near the crash site on Wednesday morning after the weather improved.

Eric Apolonio, a spokesman for the Civil Aviation Authority of the Philippines, said only the tail section of the plane remained intact, with the rest of the wreckage scattered on the barren upper slopes of the Mayon volcano.

Villagers are normally prohibited from entering a permanent danger zone around the volcano, which last erupted in 2018, displacing tens of thousands of people.

However, a monitoring agency allowed the high-risk search-and-rescue effort with a warning for team members to be alert for the sudden emission of volcanic ash and gas, or sudden mud flows if rain fell on the slopes.

The deaths of the four men were confirmed on Thursday by Foreign Minister Penny Wong.

"On behalf of the Australian government, I wish to extend our deepest sympathy to the families of the two men Simon Chipperfield and Karthi Santhanam - both from Adelaide, my home town - as well as the Filipino nationals involved," Senator Wong told reporters in Fiji.

"The families of those who we have lost will be grieving, and I express not only our sympathy and condolences, but to say to them our hearts go out to them in this time of great grief."

Adelaide-based work health and safety group Beaumont Solutions, where Mr Santhanam was also a consultant, paid tribute to him in a Facebook post.

"Karthi was an incredibly talented engineer, who had the skills and infectious optimism that we could work together to leave a better world for our children," the company said.

"He recently agreed to join our team, and in our last conversation he said renewable energy projects must be his legacy, the legacy he would leave for his children.

"We will continue to recognise his passion and contribute to that legacy in our work and our family life."

Mr Chipperfield and Mr Santhanam also both previously worked with oil and gas company Santos in Adelaide.

with Associated Press

Australian Associated Press