Papua New Guinea's former attorney general Sir Arnold Amet has criticised Nautilus Minerals' Solwara deep sea mining project in the Bismarck Sea.
The Canadian company plans to mine the sea bed off the coast of New Ireland.
Sir Arnold said no evidence had been provided from Nautilus' test site at Motukea island that its machines would not malfunction at the intended operating depth of 1.6 kilometres.
He said he was concerned that the PNG government had bought a 15 percent share in what he described as "a dodgy project," which could create an environmental catastrophe for the Bismarck Sea and its communities.
Information contained in a Nautilus Minerals annual report said both the environmental impacts and profits from the project were unknown.
Sir Arnold said the company should not have been given the right to mine.
"With this high level of environmental and financial risk, the PNG Government should never have issued Nautilus with its licence. It was issued even though PNG has no legal framework to regulate such a mine and we have no capacity to monitor its impacts."
In May, Nautilus minerals said it was confident the project was on track to start extracting ore in the first quarter of 2019.