Twenty-three protesters, including Newcastle Greens councillor Michael Osborne, were arrested and charged after blocking the line near Sandgate from 9am until 3pm.

The train driver saw the protesters on the track and stopped the slow-moving train before it crossed the Hunter River.

About a dozen eastbound coal trains were affected by the protest, while empty trains were unable to return to the coalfields from Kooragang Island.

The protesters were disappointed that the UN climate talks failed to produce a legally binding treaty to reduce carbon emissions.

They were especially critical of Prime Minister Kevin Rudd and Climate Change Minister Penny Wong.

Among them was Cr Osborne who said, "I think Kevin Rudd's pathetic" as he was led to a police vehicle.

Some protesters placed bicycle locks around their necks and attached themselves to the train.

Eighty-six year-old Bill Ryan from Wollongong was the oldest protester and one of the first to be arrested.

The most difficult arrests were of four people who hung from the bridge over the river and a man who sat about four metres above the track on a tripod.

Officers from police rescue, the public order and riot squad, water police and general duties officers attended the scene, as well as two ambulances and a NSW Maritime boat.

Acting Inspector Alan Janson said police were given no warning and were forced to dedicate a lot of resources to the protest.

Brad Emery, spokesman for the Australian Rail Track Corporation, said the protesters should think about the impact their actions have on the Hunter economy and jobs.

"Protests like this cost millions of dollars," he said.