Australia's Newcastle port has opened its third coal export terminal on Monday, strengthening the New South Wales city's position as the number one coal port in the world, but drawing protests from environmentalists.

Owner of the new port, Newcastle Coal Infrastructure Group (NCIG), took three years to complete the construction, the Australian Associated Press reported.

NCIG shareholders include major miners such as BHP Billiton, Centennial Coal and Whitehaven Coal.

They are now considering a stage two development which would increase capacity to 66 million tonnes a year. The stage one terminal can move up to 30 million tonnes a year.

The expansion is needed due to consistently strong export demand and the development will keep a workforce of about 800 busy for another two to three years, according to NCIG.

"Stage two will double the capability of stage one, adding more than A$600 million a year to state revenue through royalties and attract extra investment of more than A$1 billion to New South Wales," NCIG Chairman Tony Galligan said in a statement.

The new coal terminal has, however, drawn criticisms from campaigners for the environment.

Protesters had overnight painted "quit coal" in large white letters on the side of bulk carrier Global Splendour, which on Monday began loading coal from the Wambo mine.

Rising Tide Newcastle, which had campaigned against the terminal since it was first proposed, said the terminal's opening marked a day of protest rather than celebration.

"We are witnessing the expansion of Australia's number one cause of climate change," Steve Phillips, the group's spokesman, was reported saying.

"The coal sold from this terminal will produce as much greenhouse pollution as every power station, every steel mill, every car, truck, and bus in the state of New South Wales."