The Crossrail project will now open in the third quarter of 2019

London's new train line, which was set to open through the city centre in December, has been put back for nearly a year, the mammoth Crossrail project announced Friday.

The Elizabeth Line, 10 years in the making and set to add 10 percent to central London's rail capacity, will now open in the third quarter of 2019, Crossrail said.

"We have made huge progress with the delivery of this incredible project but we need further time to complete the testing of the new railway," Crossrail chief executive Simon Wright said in a statement.

The 73-mile (118-kilometre) east-west railway line, with two branches at either end, will bring an extra 1.5 million people to within 45 minutes of central London.

More than 200 million passengers are expected to use it every year.

Overground parts of the line in the suburbs are already operating but the main underground section through the city centre has now been put back.

A July update on the scheme said the budget was running at £15.4 billion ($20 billion, 17 billion euros).

The government believes it will add up to £42 billion to the UK economy.

Mark Wild, London Underground and Elizabeth Line managing director, said: "The delayed opening is disappointing, but ensuring the Elizabeth Line is safe and reliable for our customers from day one is of paramount importance."

The Elizabeth Line will appear in purple on the famous London Underground train map.