PERTH (Reuters) - Australia's rapid expansion of coal ports in the next decade will threaten the Great Barrier Reef as increased ship traffic, port infrastructure and dredging put pressure on the world's largest coral reef, Greenpeace said on Thursday.

Coal is one of Australia's top export earners, and the Great Barrier Reef sits off the coast of the eastern state of Queensland, the country's largest coal-producer.

"The creation of mega mines in central Queensland, the accompanying export infrastructure and increases in shipping traffic, as well as the burning of the coal they produce, place an incredible burden on Australia's Great Barrier Reef," the environmental group said in a report.

The Great Barrier Reef Marine Park, one of Australia's main tourist attractions, runs along most of Queensland's coast and is adjacent to some of Australia's largest coal ports.

Port expansion on the Queensland coast could take coal export capacity from 257 million tonnes now to 944 tonnes by 2020, Greenpeace said.

With the coming expansions, as many as 10,000 coal ships per year -- or more than one an hour -- could make their way through the Great Barrier Reef World Heritage Area by 2020, up 480 percent from 1,722 ships in 2011, according to the group.

"More ships mean more pollution, more spills, more groundings and more collisions," Greenpeace said.

In 2010, a Chinese coal ship, the Shen Neng 1, ran aground on the reef and damaged part of it.

Increased coal use also poses a threat to the reef because high carbon emissions contribute to climate change, Greenpeace said.

UNESCO DELEGATION

Although Australia recently passed a carbon tax of $23 per tonne that will kick in July 2012 with the aim of reducing fossil fuel use and emissions, the country exports the majority of its coal to Asian customers.

The Greenpeace report comes ahead of a visit this month by a delegation from UNESCO, which designated the reef a world heritage site in 1981.

UNESCO has expressed concern about the impact of the booming liquefied natural gas (LNG) industry's impact and is visiting the area to examine plans for several industrial developments.

Last month, the government said it would carry out a comprehensive assessment of development pressure on reef, which it will discuss with the UNESCO delegation.

The Australian Coal Association said it was unlikely that all the proposed coal port expansions would take place.

"The Greenpeace forecast assumes that every single proposal will come to project fruition. This is simply inconsistent with historical experience," association chief executive officer Nikki Williams said in a statement.

The association also said the reef was covered by a vessel tracking system which was not in place when the Shen Neng ran aground in 2010.

"The Australian coal industry shares Greenpeace's concern about the need to preserve the globally iconic Great Barrier Reef ... any incident that impacts the reef is totally unacceptable," Williams said.

(Reporting by Rebekah Kebede; Editing by Robert Birsel)