NSW's largest state-owned electricity generator is being put up for sale as the state government continues to offload its power assets.

Critics are expected to pounce on it as further evidence the O'Farrell government is moving towards full-scale electricity privatisation.

NSW Treasurer Mike Baird on Tuesday called for expressions of interest for Macquarie Generation's two big power stations: Liddell and Bayswater.

"Being located in the Hunter Valley, (it is) well placed to meet its long-term fuel supply needs," he said.

There's been a string of state-owned plants offloaded to the private sector after the Tamberlin report, which found their sale was consistent with a competitive energy market.

EnergyAustralia last week snapped up state-owned Delta Electricity's Mount Piper and Wallerawang power stations for $160 million.

Once the two black coal-fired stations owned by Macquarie Generation are gone there will be only a pair left on the central coast.

However, Delta Electricity's power stations at Vales Point and Colongra aren't expected to be sold off until next year.

Macquarie Generation is the largest single participant in the national electricity market, representing about 26 per cent of the state's generation capacity.

Two of its development sites will also be offered for sale, including a site adjacent to the Bayswater power station with planning approval for a coal or gas fired generator.

Mr Baird said the sell-off was part of the government's strategy to raise money for critical infrastructure projects.

The government has undertaken not to sell its most valuable electricity asset, Transgrid, the so-called "poles and wires", in this term of parliament.

But the opposition claims it's "selling off anything that isn't bolted down".

Last month it leased the Port of Newcastle for 99 years in a deal expected to net the government more than $700 million, while a similar arrangement was finalised in April for Port Botany and Port Kembla for over $5 billion.

Sydney's desalination plant was leased for 50 years in 2012 in a $2.3 billion deal.