Ministers who have given the go-ahead for a third high-speed railway link have admitted they do not know how much the new project could cost.
Officials told The Daily Mail it was "too early" to put a figure on it, although the Chancellor previously estimated it would set the government back up to £7 billion.
But there is speculation HS3 could be even more expensive per mile than HS2.
Northern council chiefs have welcomed the announcement, which could see journey times between Manchester and Leeds slashed by more than half from an hour to just 26 minutes.
However, rail protesters claim the government is "throwing good money after bad".
"I welcome today's announcement. HS2 is important strategic infrastructure but must be linked with improvements in the classic rail network to bring maximum benefit. Sir David Higgins is also clear that HS2 should be part of a wider national transport strategy, as the Transport Committee has recommended."
"These proposals are a welcome boost to Northern economies and should be followed by investment following discussions with local authorities and businesses."
Nick Clegg, Deputy Prime Minister and Liberal Democrat MP for Sheffield Hallam, has commented on today's HS2/HS3 announcement.
"I strongly welcome the fact that this report lays to rest, once and for all, the claims made by those who don't believe that high speed rail should pass through south Yorkshire by way of the eastbound link."
"I also welcome David Higgins' call for all communities and local authorities in the north of England to work together to develop plans for better east-west links. There's no point developing north-south links without promoting the connectivity of the cities in the north."
"As a Sheffield MP, it is essential to me that this is not just confined to improving connections between Manchester and Leeds, but helps us in Sheffield and the whole of the north of England too."
As part of the Government's long term economic plan for the north, the Prime Minister and Chancellor gave their backing to develop HS3 - connecting the north's cities which they say could significantly reduce journey times across the region.
"Improving connectivity and reducing journey times between our great northern cities is a crucial part of our long term economic plan for the north to boost businesses and create more jobs and security for hardworking people. That's why we are backing HS3."
"The vision I set out earlier this year of the Northern Powerhouse we could build is rapidly taking shape. I asked Sir David Higgins to look at how we deliver the better transport links across the north that would make a reality of that powerhouse."
"I am delighted with the rapid response and the report. Today we take another big step forward in delivering both the HS2 links from north to south and the HS3 link across the Pennines."
Transport Secretary Patrick McLoughlin has the development of the HS2 high-speed railway project linking northern cities will "benefit the UK overall".
"Knowledge based companies whether they are in high-tech manufacturing, the creative industries, finance or the law, have to be close, or feel close to the talent, skills base, support network, knowledge pools, collaborators and clients necessary to create the "hot-house atmosphere" in which they thrive. That is why reducing the journey times between and within our cities isn't just desirable for both passengers and freight. It is a strategic necessity."
"Without question HS2 is the key to transforming the future economy of Leeds and the north. It offers huge benefits in terms of job creation and opportunities, driving growth and innovation and bringing people and places closer together making cities like Leeds and the wider city regions much more attractive for businesses to base themselves."
Train journey times between northern English cities could be slashed by half after ministers backed plans for a third high-speed railway.
The proposals were put forward in a report from the head of the £50 billion HS2 high-speed rail project, Sir David Higgins.
The improvements would cover an east-west section of northern England and would be in addition to the north-of-Birmingham phase two of HS2 which will see a Y-shaped route going to Manchester and Leeds.
Sir David said northern connectivity plans - dubbed "HS3" and backed by Chancellor George Osborne - would be "as important to the north of England as Crossrail is for London".
If carried forward, the plans would mean journey times between Leeds and Manchester could almost be cut in half.
While journeys between Leeds and Birmingham, Leeds and Sheffield Meadowhall, York and Birmingham and Nottingham to Birmingham could also be reduced by a half or more, and many more journeys across the country substantially shortened.
"Improving connectivity is vital if Britain is to compete in the knowledge economy in which this country has a competitive advantage, but in which ease of travel is an essential element."
New details have been released about how train journeys across the Pennines could be speeded up.
A report commissioned by the Government is recommending a new high speed railway line. Average times for going between Leeds and Manchester could be reduced from 55 minutes to as little as 26 minutes.
A house of Lords committee has launched an inquiry into the economic case behind the proposed High speed 2 rail project.
The inquiry will consider the economic benefits of the scheme and whether London will be the main beneficiary. It will investigate the likely benefits of HS2 to our region and whether some parts of the country could lose out from the scheme.