CLIMATE militants staged a 30-hour blockade at Newcastle, NSW, the nation's biggest coal export harbour, Reuters reports.

Rising Tide militants, which claimed responsibility, said more than 200 protesters were in the shipping channel near the Port of Newcastle.

The Port of Newcastle, 170 kilometres from Sydney, is the largest bulk shipping port on Australia's east coast.

"At present, due to the number of people currently in the shipping channel, all shipping movements have ceased due to safety concerns, irrespective of the cargo they are carrying or intend to load," said a port statement.

Rising Tide spokesman Zack Schofield said no coal shipments had entered or exited the port.

"So far it's holding true," he said of the blockade comprised of a flotilla of kayaks by the group, which carried out an unlawful protest near the same port in April when 50 activists were charged by police.

State police said no arrests had been made in relation to the protest under way near the port on Saturday.

The leftist Labor government does not support a ban on all new fossil fuel projects, but sees "safeguard mechanism" reforms as key to cutting emissions by 43 per cent by 2030 in a country that ranks as a leading global carbon emitter per capita.