Six Greenpeace activists who boarded a coal carrier heading from Australia to South Korea have left the vessel after a cold and uncomfortable night on the ship's deck.

The environmentalists boarded the MV Meister on Wednesday morning in the Coral Sea, northeast of Townsville, in a protest against Australia's increasing coal exports.

Greenpeace activists board a ship in the Coral Sea. Credit:Greenpeace

After spending a "wet, cold and uncomfortable" night on the deck, the activists used the ship's ladder to descend to inflatable boats and were taken back to the Greenpeace flagship Rainbow Warrior.

The Meister's captain had slowed the vessel to allow the activists off the ship.