Australia's Northern Territory has begun one of the largest mass evacuations since 1974 as two powerful storms threaten the country's northern coastline.

Tropical Cyclone Trevor, which lashed Cape York communities this week, is regaining strength as it moves over the warm waters of the Gulf of Carpentaria.

The category one system is expected to reach category four strength by the time it crosses the Northern Territory coastline somewhere between Port McArthur and Port Roper (about 725km and 550km south-east of Darwin respectively) on Saturday (March 23) morning, reported The Australian.

Meanwhile, Severe Tropical Cyclone Veronica, presently in the Indian Ocean waters north-west of Broome, is predicted to reach category five strength and turn south towards the Western Australian towns of Karratha and Port Headland over the weekend, the newspaper said.

Forecasters have not ruled out Trevor also becoming a category five storm. Emergency Services and the Australian Defence Force are involved in evacuating several thousand people from communities in the region, The Australian said.

NT Chief Minister Michael Gunner announced on Thursday morning that he had declared a state of emergency.

"It is really important that you stay informed... and take this seriously, not just the cyclonic winds but the storm surge that comes with them," Mr Gunner said.

Regional Controller Travis Wurst warned residents that Trevor was a "significant and serious weather system".

"If this weather event moves faster and impacts on our ability to use road, we will then look at air evacuations," Mr Wurst said.

Between 500 and 600 people have already been evacuated to Darwin and Katherine, with more expected to follow.

The Australian Defence Force (ADF) is flying more residents from Groote Eylandt to Darwin on Thursday after transporting residents into the city the day before, reported broadcaster ABC.

Lieutenant Colonel Scott Jamison told ABC Local Radio the ADF was "prepared to evacuate a couple of thousand (people) in support of the government".

"At the moment we've got four aircraft in the air... In the last 24 hours, there's been hundreds of people involved in the planning, from Northern Territory government, the local Defence Force personnel up here in Darwin, also Defence headquarters down in Canberra," he said.

Northern Territory Police, Fire and Emergency Services incident controller Hege Burns said local charter companies and Airnorth evacuated about 220 of the island's 1,600 residents yesterday, and the ADF would ramp up those efforts today.

At dawn, nine buses were due to bring residents from the coastal community of Numbulwar to Katherine, and buses will continue running throughout the day.

On average, there are 10 to 13 tropical cyclones each season, four of which typically cross the coast, according to the Bureau of Meteorology (BOM).

The current Northern Territory cyclone watch area is thought to be home to about 10,000 people, ABC said, with about 5,000 in the most at-risk area from Groote Eylandt to Borroloola.

Overnight, Trevor lashed communities on Queensland's Cape York with powerful gusts and heavy rain.

BOM forecaster Gabriel Brenescu said Trevor would intensify quickly and could develop into a category five system over the next two to three days.

BOM said wind gusts higher than 130kmh could develop between the Cape York towns of Weipa and Aurukun on Thursday as the system strengthened.

The heavy rainfall and gale force winds have also impacted other parts of Far North Queensland with a land slip at Barron Gorge bringing down trees and boulders.

Douglas Shire Council have warned residents not to cross flooded roads and bridges after rapid river and creek rises in the last 24 hours.

Mining operations brace for impact

Gas and iron ore operations on Australia's west coast are also bracing for Veronica just as Trevor dumps heavy rain on Rio Tinto Group's biggest bauxite mine, Bloomberg reported on Wednesday.

Port Hedland, which is in Veronica's path, is a key export point for Western Australia's iron ore shipments. The storm is forecast to intensify as it moves closer to oil and gas operations on Saturday, according to the BOM.

In the east of the country, Rio has suspended its Weipa bauxite operations after cyclone Trevor made landfall, Bloomberg said.

Cyclone Trevor is expected to rapidly strengthen as it moves into the Gulf of Carpentaria, and is forecast to skirt South32's manganese mine on Groote Eylandt and a Glencore-operated zinc project as it makes its way towards the Northern Territory coast.

South32 will start evacuating workers from the island, a spokesman said.

Woodside Petroleum, which operates the North West Shelf liquefied natural gas project near Karratha, said it is taking precautions to safeguard its people and assets.