Papua New Guinea's Maritime Union has called on Prime Minister Sir Michael Somare to have a ship certification company he allegedly owns shares in, deregistered.

Radio Australia's Firmin Nanol reports the Pacific Registry of Ships was incorporated in November 2004 to do safety surveys on ships.

Prime Minister Sir Michael Somare's office has admitted he holds shares in the company, in trust for the state.

The PNG's Maritime Workers Union claims the firm, does not carry out proper safety checks on ships putting passengers' lives and vessels at risk.

Spokesperson, John Mahuk says the Prime Minister should have the ship certification company deregistered.

"That company has to be removed," he said.

"It is duplicating the roles and functions of the national maritime safety Authority in charge of inspections and surveying of all the ships that come into the country."

Meanwhile, the Maritime Safety Authority's Chris Rupen has admitted Pacific Registry of Ships is not trustworthy.

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