The New South Wales Rural Fire Service has unveiled its newest firefighting tool, a massive water-bombing aircraft nicknamed Thor, ahead of the bushfire season.

The plane has just arrived from North America for the Australian bushfire season and performed a practise water-bombing exercise near Richmond air base in north-west Sydney.

The air tanker can drop more than 15,000 litres of water or fire retardant on a blaze within a few seconds.

It has a loaded cruising speed of 545 kilometres an hour, meaning it will be able to reach most fires in the state within one hour.

Emergency Services Minister David Elliott said the aircraft would be a welcome sight for residents in fire-prone areas.

"The people of NSW will be able to rest easy tonight, the first day of spring, knowing that Thor will be in the skies looking out for them," Mr Elliott said.

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RFS Commissioner Shane Fitzsimmons said the specially configured C-130 Hercules will dwarf the capability of the smaller water-bombing planes in the fleet.

"This can carry five times the water of those machines," he said.

"They can take off and land on airstrips of less than two kilometres, they're very versatile."

The plane's pilot, Rickey Rau said Thor can fly fully loaded for at least five hours.

"Depending on where the fire is, we can launch out of here fully loaded and do two to three runs on the fire before needing fuel," Mr Rau said.

The plane will be based at the Richmond air base, but could also be moved to smaller bases at Williamtown, Tamworth, Dubbo and Canberra.

A C-130 Hercules dubbed Thor has been converted into a water-bomber to help fight bushfires. ( ABC News: Nick Dole )

The aircraft will be leased to NSW for two fire seasons as part of a $10 million State Government funding package.

An ever bigger DC-10 air tanker will arrive in October.

Commissioner Fitzsimmons said much of NSW was facing an "above normal" risk of bushfires this season.

"That's largely caused by the moisture deficit," he said.

He said there has been solid rainfall in recent months, but it was not likely to have a lasting effect.

"With the onset of a strengthening El Nino still dominating the forecast for this season, the moisture is expected to be depleted fairly quickly, giving rise to a difficult fire season for 2015/16," he said.