According to reports, they entered an airtight compartment of a shipping barge to inspect its damaged bow and died of suffocation after being caught unawares of the change in depth-pressure.
PNG police said Australian dive operator Stephen Woolcott was one of the men killed in the accident yesterday.
Reports from local media and police suggested the men entered the airtight compartment of the large shipping barge Colossus to inspect damage to the bow.
They reportedly lost consciousness due to a lack of oxygen.
Local media reports said three of the men killed were from the Nivani construction company, but police could not confirm details of the locals killed.
Mr Woolcott was born in Rabaul and was well known for running the Kabaira Dive Centre.