State Treasurer Mike Baird said the expressions of interest, which are being run by financial adviser Morgan Stanley, will allow the government to shortlist the most qualified parties and invite them to submit final proposals.

"The overriding objective is to ensure that we select the most suitably qualified party or parties to lease the ports, which will free up much-needed capital to help us fund the backlog of critical infrastructure across the state," Mr Baird said.

He reiterated the government's pledge to reserve $100 million from the leasing of Port Kembla for infrastructure projects in the Illawarra.

The remainder of the proceeds will be invested in the government's infrastructure fund, Restart NSW, with 30 per cent of funds reserved for projects in regional areas.

Mr Baird said the government, through the Port Kembla Port Corporation, would retain regulatory oversight of the port and responsibility for maritime safety - such as harbourmaster duties - and security functions.

There has been interest in the leasing from Australian and overseas bidders, which is understood to include North American superannuation groups.

Mr Baird said Port Kembla and Port Botany were appealing assets for prospective bidders.

"Port Botany is the gateway to Australia's largest economy and is Australia's second-largest container port, and Port Kembla offers a diversified revenue base with bulk products including grain, steel, coal and iron ore and is Australia's largest vehicle-import hub," Mr Baird said.

"A private lessee will be better able to invest in long-term growth . . . allowing the government to focus on delivering critical road, school and hospital projects across NSW."