Scott Morrison has savaged a draft recommendation from UNESCO to list the Great Barrier Reef as "in danger".
The federal government suspects China has used its political clout on advisory bodies to engineer the outcome.
Various delegates to UNESCO from around the world have now co-signed an open letter denouncing the reef recommendation.
"The UNESCO process has been appalling," the prime minister told Brisbane radio 4BC on Thursday.
"We've been busy in talking to our friends and the list of countries is quite extraordinary."
UNESCO insists its recommendation is based on science, not political influence.
But Mr Morrison is furious about the apparent lack of transparency, due process and consultation.
"This process is not on. There's a proper way to do these things," he said.
"We invest, together with the Queensland government, some $3 billion on reef sciences, the best managed reef in the world.
"Sure, it's got challenges like sensitive environments all around the world, but Australia does it better than anywhere else, so we will be making that case."
The prime minister believes there has been a significant shift in UNESCO's approach.
"We really do think this process has been absolutely appalling, quite different to when this issue was dealt with by UNESCO early on in our government back in 2014," Mr Morrison said.
"We worked through that process and got the right outcome, but this process is a bit of a try-on."
