A foreign flagged cargo ship is being held over alleged safety breaches so bad that it was at risk of sinking.

The Orient Becrux has been inspected by Australian Maritime Safety Authority officials in Newcastle, after unions blew the whistle.

Reports say the ship has been found to have breached the International Convention for Safety of Life at Sea.

Union officials allege that the Hong Kong-based charter company made the ship's crew unlash the cargo at sea.

However, the International Transport Workers Federation says the load could only be unfastened by qualified Australian stevedores, and while the ship is berthed.

The cargo included heavy rail cars and other vehicles, the unfastening of which would have put the entire crew's lives at risk.

The shifting cargo could have easily brought down the ship.

The Australian Maritime Safety Authority says it is awaiting a report from its surveyors, who been conducting close inspections on board the vessel.