More than 25,000 litres of heavy oil spilled into the harbour just before midnight on Tuesday after a tugboat struck and split open the fuel tank of a Panamanian-registered but Korean-owned bulk carrier, the Global Peace.

The tugboat was helping the carrier berth at Gladstone’s coal terminal, which is on track to become the world's largest coal export facility.

It was the second spill in Gladstone's harbour within a week. The clean-up is expected to take up to a week and cost more than $3 million.

The Wildlife Protection Association of Australia (WPAA) says the spill will be devastating for sensitive mangrove swamps and estuaries and local marine life.

Once the oil gets in among the mangroves it is very difficult to clean up and the area has dugongs, crocodiles, turtles and seabirds and many more animals that will be affected by the spill.

The Australian Maritime Safety Authority and the Australian Transport Safety Bureau have launched inquiries in to the spill. The ATSB says preliminary investigations into the spill should be completed by this afternoon.

The local commercial fishing industry also wants to know how a tug boat could pierce the hull of a bulk coal carrier.

The marina is closed to vessels, preventing the unloading of valuable but perishable catches and leaving other fishermen stranded on shore. Fishermen say that lack of access is costing them thousands daily, pushing the local industry to the brink of collapse.

Fishing industry spokesmen said they also feared the impact of the spill on the local food chain and were worried that it could take years for the area to recover.

Australian Safety Transport Bureau launched investigations into the spill.

Queensland Transport Minister Paul Lucas said he was confident of the best possible outcome.

"Many of the people involved have worked on oil spills all over the world and train regularly for these types of incidents," Lucas said.

NSW Ports Minister Eric Roozendaal said two experts from the Sydney Ports Corporation had been sent to Queensland as part of a national response to the spill.