Expressions of interest for developing hydrogen production in the Hunter and Illawarra, currently "coal country", have attracted more than $4 billion in proposed private sector investment.

Treasurer and Energy Minister Matt Kean says "the market has spoken".

"This is an overwhelming level of commercial interest and it shows our policies are sending the right signals to energy investors, making NSW the go-to state for energy investment," Mr Kean said.

The initial plan targeted 700 megawatts of production, but proposals before the government could produce up to 5900MW.

The hubs were part of a $70 million commitment in the NSW hydrogen strategy launched in October last year.

Acting Premier Paul Toole said they will help secure jobs into the future and also provide huge export potential as the demand for hydrogen rises globally.

The 21 proposed projects could produce up to 268,000 tonnes of "green hydrogen" annually.

Unlike "blue hydrogen" that relies on gas, the green hydrogen is produced using renewable sources such as solar and wind.

Mr Kean said green hydrogen will play an important role in decarbonising heavy industry and transport, and the proposals for the hubs could fuel 26,000 trucks.

On Friday, NSW, Queensland and Victoria announced plans for a hydrogen refuelling network across the Hume, Pacific and Newell Highways.

Last year, the state's largest gas supplier, Jemena, began blending green hydrogen into its gas network from a facility in Sydney's west, powering homes, commercial and industrial sites.

That facility, co-funded by the Australian Renewable Energy Agency is also expected to provide hydrogen for transport uses this year.

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