The Shen Neng 1 ran aground on Saturday when it hit a shoal off the eastern state of Queensland at full speed, rupturing a fuel tank and causing a three-kilometre (almost two mile) long slick on the World Heritage site.
"One of the most worrying aspects is that the ship is still moving on the reef to the action of the seas, which is doing further damage," said the general manager of Marine Safety Queensland Patrick Quirk.
Salvage experts have boarded the Chinese-registered carrier, which is loaded with 65,000 tonnes of coal and about 975 tonnes of heavy fuel oil, stranded some 70 kilometres east of the resort destination Great Keppel Island.
One tug boat is already at the scene to stabilise the vessel and another will arrive later Monday, while aircraft are being being used to monitor the spill in waters teeming with marine life.
"The hope is that little oil escaped through the night," Quirk said.
The vessel hit Douglas Shoal, which is at the southern end of the Great Barrier Reef Mari