*Government makes first down-payment on City Rail Link, will pay its full share by 2020

*$450m for Kiwirail infrastructure and rolling stock

*$98.4m for upgrade Wellington's metro rail

The Government has begun paying for its share of Auckland's City Rail Link, committing $436m towards the project in today's Budget.

It committed last year to paying for half of the 3.4km rail line, which has an estimated cost of between $2.8 billion and $3.4 billion.

The remainder of the Government's investment in the City Rail Link (CRL) would be paid off in the next three Budgets, Transport Minister Simon Bridges said today.

Bridges said the project was Auckland's "top new transport priority" and was already bringing economic benefits by creating hundreds of construction jobs.

The double-track underground line will run from Britomart Station in Auckland's CBD to the existing western line in Mt Eden.

It is expected to double the capacity of the Auckland Metro Rail network and cut travel times for commuters. Rail patronage in Auckland is increasing by around 22 per cent a year.

Another $450 million has been invested in the state-owned rail company Kiwirail in the Budget, which will be allocated over the next two years.

There are few specific details about how the money will be spent, but Bridges said it would go towards making rail infrastructure and systems more reliable and resilient. The Government wanted the rail network to be on a longer-term, sustainable footing, he said.

Budget 2017 also includes nearly $100 million for Wellington's metro rail network, which would mostly go towards replacing poles and wires for trains on the Hutt Valley, Melling and Johnsonville rail lines.

As already announced, $812m will go into rebuilding State Highway One north and south of Kaikoura, which was covered by land slips in the November quake.