Private consultants providing less than "best value" has contributed to cost blowouts on Sydney Metro projects, an inquiry into the multi-billion-dollar Metro West project has heard.
The Minns government has put aside $13.7 billion over four years for the project - first announced in 2016 by the former coalition government - after warning this year costs had overrun by $12 billion, to a total of $25 billion.
The merits of the line from the city centre to Parramatta are being examined by an independent review and a Labor-chaired parliamentary inquiry, with the government refusing to guarantee the underground rail line's future.
On Friday, NSW Auditor-General Margaret Crawford was quizzed on whether the state was getting "good bang for buck" for its use of consultants on the troubled project and if they had contributed to its ballooning costs.
While no specific audit of Metro West had been done, Ms Crawford said her office had done work in relation to agencies' use of consultants that pointed to poor management.
The analysis of 10 state agencies, including of Sydney Metro, showed "best value was not necessarily being achieved from the use of consultants", she said.
The Audit Office in March estimated NSW spent at least $1 billion on outsourced advice in the four years to 2021.
Earlier, Labor's Warren Kirby told the inquiry the Metro West project risked repeating errors made with Metro North West, which opened in 2019.
Mr Kirby, the MP for Riverstone, urged more consideration of liveability in high-density areas close to metro stations, which he said had failed with the line through the city's northwestern suburbs.
"It's an unmitigated disaster," he said of the project's fit in the region where most residents still owned at least two cars.
The NSW government has referred the Metro West to the committee to examine its original business case, how the route and station locations were selected and the cause of cost and timeline blowouts.
Stations on the 24-kilometre line are proposed for Westmead, Parramatta, Sydney Olympic Park, North Strathfield, Burwood North, Five Dock, the bays precinct, Pyrmont and the city centre.
City of Sydney Lord Mayor Clover Moore called for the line to be extended eastward with a stop at Zetland given a significant transport infrastructure deficit at Green Square.
"I made it clear to the previous government that Sydney Metro West continuing out to Zetland is essential and should be delivered as soon as possible," she told the inquiry.
Ms Moore said with up to 70,000 people set to live in the area by 2036 it was urgent to extend the metro to avoid further congestion on the at-capacity airport link.
Sydney Metro chief executive Peter Regan defended the project, saying it was part of the "critical backbone" of the broader $60 billion metro network.
However, he declined to hand up business cases for Metro West because they were cabinet-in-confidence documents.
