The Turnbull government will spend nearly $7 billion on massive, long-range surveillance drones that will dramatically expand Australia’s ability to spot military ships on the seas of Asia and tighten joint operations with the United States in the region.

Prime Minister Malcolm Turnbull will on Tuesday announce the purchase of the country's first Triton drone, which has the wingspan of a Boeing 737 and will easily be able to complete a lap of the South China Sea after taking off from the Northern Territory.

Australia will purchase at least six MQ-4C Triton drones. Credit:Department of Defence

Australia will work with the US on the drone program, and the RAAF’s eventual fleet of six Tritons will operate closely with the United States on shared missions as needed.

“Australia’s alliance with the US is our most important defence relationship, underpinned by strong co-operation in defence industry and capability development,” Mr Turnbull said in a statement.