The state government has announced it will build and open a new train station in Perth’s outer suburbs as it fights to keep its hold on Secret Harbour ahead of the upcoming byelection.

Premier Roger Cook announced the $156 million train station for Karnup on Sunday, with Transport Minister Rita Saffioti confirming she would be allocating $10 million to begin planning the station.

Karnup is in the Secret Harbour electorate, which used to be held by WA Defence Minister Paul Papalia before he announced his retirement last month. Running in his place is Labor candidate Georgia Tree, who previously came under fire for living outside of the electorate. She has since moved in with family to stay inside her voter base.

Karnup train station was first flagged for the Mandurah Line back in 2013, and has faced extensive delays since.

Cook said on Sunday population growth in the southern suburb meant the Karnup train station was now top of their agenda.

“As part of our long-term MetroNet vision, we have always planned for a train station here at Karnup, and today we can announce work will start on the Karnup train station project in 2028,” he said.

Cook said WA’s share of the project would be funded by land sales, while they would seek the other half from the federal government.

Transport Minister Rita Saffioti said the train station was “always part of the plan”, but accepted the project had been sped up by the upcoming byelection.

“In relation to the timing, look, we would probably have made this announcement over the next six to eight months, but of course we have bought that announcement early,” she said.

“Because we have got so much certainty now with the planning ... it’s all coming together.”

Saffioti said the project had been initially held up due to zoning laws and funding issues, due to the prioritisation of the nearby Lakelands train station.

Ultimately, Saffioti said the station would be an “elevated design” with more than 400 car parking pays and an eight bus interchange.

The Labor government’s announcement comes just five days after opposition leader Basil Zempilas said he would be looking to revive the project if elected.

“Labor promised Karnup Station in 2013, again in 2017 and again in 2021. Nearly a decade after Labor came to government, there is still no money in the State Budget, no construction timetable and no delivery date,” he said.

“Locals have waited long enough. They deserve a firm commitment, not another promise designed to get Labor through an election.”

Zempilas said the Liberals would commit $90 million to the project and commence building in 2029, and Saffioti slammed the figure as “undercosting”.

“There’s no way they’ll deliver it for $90 million,” she said.

“Look, they said they’ll deliver an Ellenbrook rail line in 2008, and they never did. They said they’ll deliver max light rail. They came out with a under-costed ‘back of the envelope’ commitment.”

Liberal local candidate Ryan Robertson offered his own support for the project, but said only his party had listened to residents about what they wanted from the train station.

“People in Secret Harbour and surrounding suburbs are tired of being told Karnup station is coming,” Mr Robertson said.

“They have watched Labor make the same promise election after election while the station has remained unfunded and undelivered.

“Karnup station is essential infrastructure for the future of this fast-growing community.”