London's Crossrail project is running almost £600m over budget with extra funding required to complete the work, the rail minister has announced.
Jo Johnson revealed the scheme's budget had increased from £14.8bn to £15.4bn in his annual update about the project.
Mr Johnson said "cost pressures" had risen but additional finance will be provided by the Department for Transport (DfT) and Transport for London (TfL).
Crossrail is due to open in December.
A spokesperson for the project said that while the cost increases were "disappointing" the extra funding "is critical to the delivery of this vital project".
The DfT and TfL are each providing £150m of additional funding to complete construction of the scheme.
An extra £290m will also be paid by the DfT and Network Rail to upgrade the existing rail network linked to the project.
In his statement, Mr Johnson said the project was 93% complete and was entering "the critical testing and commissioning stage".
He said in spite of the extra funding, more than 60% of the project had been provided by Londoners and London businesses.
TfL said the the railway had "involved some of the most complex engineering ever undertaken in Europe" and "a number of factors" made the additional funding necessary.
A spokesperson for the DfT said Crossrail would add "up to £42bn to the UK economy" and the final budget was still "significantly below the original funding package of £15.9bn."
However, think tank IPPR North said the announcement about the increased funding will be "poorly received by people in the north... who are yet to see the investment that we need."
Liverpool City Region mayor Steve Rotheram claimed the increase in Crossrail's budget could fund "a significant amount of a new west to east rail line to Manchester."
Groups in the north have previously spoken of their "widespread anger" following the government's backing of Crossrail 2.
When it opens in December, Crossrail trains will operate on three routes before the line fully opens at the end of 2019.