Boris Johnson has praised plans for Northern Powerhouse Rail (NPR) as "very, very exciting" but maintained the costs of the HS2 project need to be looked at.
The Tory leadership front-runner made the comments as he visited the construction site at Manchester Airport's new Terminal 2 extension, which is expected to open next year.
Bosses at the airport have made it clear to Government they want both Northern Powerhouse Rail (NPR) and HS2 to happen and provide a "global gateway" for the north with quicker and more frequent rail journeys to the airport.
On Tuesday, Mr Johnson was enthusiastic about the case for NPR as Transport for the North chief executive Barry White and Manchester Airport group chief executive Charlie Cornish outlined its benefits.
He later told reporters:
Mr Johnson appeared more cautious on the merits of HS2 and said there was "a legitimate question to ask about how the money is being spent".
Asked whether his stance had anything to do with HS2 running through his constituency, he said:
Mr Johnson asked for a review of the HS2 scheme by its former chairman Douglas Oakervee, which is due to be completed by December.
The extended departure terminal at Manchester Airport will more than double in size as part of the airport's £1 billion transformation. The first phase of the programme opened in April with the launch of a new passenger pier and a 3,800-space multi storey car park.
When the terminal extension is complete and opened the existing Terminal 2 building will close for refurbishment before it will be fully operational by 2022.