In August, Roads and Freight Minister Duncan Gay said the government would move to gauge private sector interest in building the 35-kilometre rail line that would start from Maldon and head south to join the Moss Vale-Unanderra line at Dombarton.

The chance for the private sector companies to register their interest began on October 13 and will continue until February 24.

A spokeswoman for Mr Gay said the NSW government did not intend to disclose information on interested parties or the level of response while the registration of interest process was continuing.

After the closing date, companies that had expressed an interest would be listed online. Applications that best addressed the selection criteria would be asked to submit a formal tender.

The project would be fully funded by the private sector and no government money would be contributed towards the construction.

The spokeswoman declined to say whether the government had any contingency plans in place should there not be much interest from the private sector.

"The [registration of interest] process is designed to inform the NSW government about the level of private sector interest in the Maldon to Dombarton railway," the spokeswoman said.

After the registration period closed, all registrations of interest would be evaluated and the results would determine the next steps, she said.