More than 2 tonnes of heavy fuel oil spilled from the Shen Neng 1 on Saturday after it hit a shoal inside a restricted zone of the Great Barrier Reef Marine Park. Authorities no longer believe it is at serious risk of breaking up but say that could change if the weather worsens.

Queensland transport department spokesperson Mark Strong is reported to have said that dispersant sprayed onto the slick has worked and the oil has broken up.

"The slick that was there has responded to the treatment and there have been no further additional spills," he said this morning.

Maritime Safety Queensland general manager Patrick Quirk said helicopter surveillance this morning showed a thin oil sheen near the ship measuring 600 metres by 300 metres.

A floating boom will be placed around the Shen Neng 1 today to contain any further leaks.

The 230-metre Shen Neng 1 was en route from Gladstone to China when it ran aground, almost 30km from the shipping channels it should have been using.

Federal authorities have launched an investigation and will look into reports the ship may have been taking a shortcut out of Australian waters.

The Great Barrier Reef Marine Park Authority says ships have been caught and prosecuted in the past for taking shortcuts through the reef.

Senator Brown says there is speculation that oil and coal tankers are moving illegally through the lane near the Douglas Shoal.

"Nothing has been done about it by the authorities," he told ABC radio.

"Now that is one of the matters that needs to be cleared up and I will be busying myself today to establish where the Australian Federal Police are in their enquiries about how this disastrous situation has arisen.

"The Queensland press is reporting today that fishermen say they see at least one of these large bulk carriers moving illegally through to the south of Douglas Shoal each day."

The Greens leader also called for a complete review about the number and size of ships moving through the Great Barrier Reef.

"This is the $60 billion a year, largely foreign-owned coal industry that is making a coal highway out of the Great Barrier Reef," he said.

"Secondly, there needs to be pilots aboard and there needs to be very strict laws including monitoring of where these ships are.

"They should be checked before they leave port to see that they are, where they are going and if they are seaworthy and that they are properly able to handle the conditions.

"There needs to be a radical overview of where this huge coal export industry, whether these ships need to use the reef at all and what the alternatives are."