New Zealand's largest ever transport project, Auckland's underground City Rail Link, has assured the government it is on track for completion by 2024 despite problems with its previous contractors.
The $3.4bn railway construction project has had difficulty retaining contractors.
Fletchers pulled out in February last year, and in December Australian-based engineering firm RCR Tomlinson also went into administration forcing City Rail Link to pull its $500m contract with RCR's New Zealand-based subsidiary.
City Rail Link told the Transport and Infrastructure Select Committee at its annual review it was confident it could fill its biggest contract yet, which would be "in excess of $1 billion".
"We've got two very credible bidders who are capable of delivering what we need according to the timelines we've established, so there is no short-term capacity issues for us," City Rail Link chair Sir Brian Roche said.
The new contract is a combination of the one left empty when RCR went into receivership - which includes the rails, power, controls and safety systems - and the building of the tunnels and stations, which City Rail Link called the "grand alliance".
The alliance approach means less risk to the contractors, because "all participants take collective ownership and equitable sharing of all risks associated," the NZTA website says, but City Rail Link chair Sir Brian Roche admitted it had been difficult for the company to find contractors.
"We are under some pressure, there is pressure of availability of contractors. We compete in the international market, which is with Australia - Australia in Melbourne, Sydney and Brisbane has a significant volume of work ... the market is stretched."
That shortage was despite the roading sector warning of lay-offs as large roading projects finish up.
Civil Contractors chief executive Peter Silcock said it was difficult for the industry to transition to the government's new transport priorities.
"This huge swing from State Highway construction to public transport has certainly been a difficult transition for the industry and a transition we're still in," he said.
"Contractors are used to switching between different activities but people do build up expertise ... someone working on the road doesn't necessarily have those skills to work on rails so it takes time to transition people across."
Minister Twyford said he did not expect there to be any problems with the contract up for tender.
"I'm not aware that there is any money being lost because of any delay at the moment," he said.
"They're just working through the issues, they're taking a new approach to the contracting, they've moved to an alliance model and there's every reason to think that will work perfectly fine, I think."
City Rail Link is expected to announce the cost and the contractor for the contract by the end of May.