Premier Gladys Berejiklian has rebutted suggestions her promise to spend $4.6 million planning fast rail in NSW is an election stunt, saying her government could not afford to wait for the federal government before starting work on the scheme.

Ms Berejiklian said on Tuesday she would start "work" on a fast rail network in the next term of government after appointing a British rail expert to consider four potential high-speed routes between Sydney and regional centres.

But after years and thousands of pages of reports and studies into the viability of high-speed rail on Australia's east coast, Ms Berejiklian rejected suggestions the pre-election announcement was aimed at marginal seats in the state's regional areas.

"Far from it. This is a government getting on with what it does well," she said.