The choppers leased from Sunshine Coast-based company McDermott Aviation Group were involved in the tragedy as they fought the blaze west of Athens.
Two crew members - a Greek and a Danish national - onboard one of the helicopters died after it exploded and crashed following the mid-air collision, Greek state broadcaster ERT said.
The other chopper, with two crew members reportedly from Greece and Great Britain, managed to make an emergency landing.
Five people have now died in the Greek blaze after three firefighters were killed on Crete and the Peloponnese peninsula last week.
McDermott Aviation confirmed two of their choppers were involved in the fatal crash that occurred near Psatha on Sunday (local time).
"We are deeply saddened to confirm that the two crew members aboard one of the helicopters have lost their lives," McDermott Aviation founder and president John McDermott said in a statement.
The other chopper's surviving crew members were in the care of medical professionals, he said.
"Our thoughts and deepest condolences are with the families, friends and colleagues of those affected by this tragic incident," Mr McDermott said.
"Both crews were undertaking the critical work of supporting firefighting operations to help protect communities."
He said McDermott Aviation was working closely with authorities and would continue to assist during the investigation into the tragedy.
ERT aired footage appearing to show one helicopter's rotor striking the other aircraft before it exploded and crashed in a fireball.
The bodies from the helicopter that crashed were later recovered after a large-scale search and rescue operation was launched in the area.
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