“Protesters stood on the rail line and climbed on top of the first train wagon, which was leaving the Maules Creek coal mine in Narrabri for Newcastle,”AAP reported.

“Two men, 36 and 45, and two women, 23 and 24, were arrested about 5.30am on Monday.”

However, Whitehaven clarified that the project was not yet railing coal to the port.

“The train involved in this protest incident was undertaking pre-commisioning tests of the new rail spur,” a spokesman told ICN.

The pace of Maules Creek construction is beating expectations though.

Earlier this month the $767 million Maules Creek project was considered more than 70% complete and more than two months ahead of schedule with first coal exports expected to be railed in January instead of March.

The open cut project is targeting a rate of 6 million tonnes per annum of coal production over the first 12 months and has approval to ramp up to 13Mtpa run of mine.