"Today changes Auckland for ever. The CRL is the heart of dealing with the city's growth, with propelling our economy, and creating a future Aucklanders want."
Mr Brown said the rail link would provide the "single best solution" to meet the demand for access to the city by allowing the movements of 30,000 people an hour during peak travel times.
Auckland Transport is forecasting an 88 per cent increase in rail patronage into the city the CRL's first year of operation and a 40 per cent increase in rail passengers across the network in the morning peak.
Mr Brown said more than 70 new private projects worth $7 billion are expected to be built around the CRL and completed by the time the link opens in 2022/23.
"The CRL has been my number one priority since becoming the first Mayor of the united Auckland. Today I am very incredibly proud to stand together with the Prime Minister and Minister of Transport to together ensure this project proceeds for the future benefit of all Aucklanders," the mayor said.
And campaigners are using the start of the project to urge officials to extend the rail network to the North Shore.
Campaign for Better Transport spokesman Cameron Pitches said the time is right to start planning to extend the rail network to the North Shore.
"It seems obvious that a high capacity, low carbon emission electric rail link across the Waitemata will do far more to move the thousands of people necessary at peak times each working day.
Mr Pitches said a road-only tunnel between Victoria Park and Esmonde Rd was estimated to cost between $4bn and $6 billion while smaller diameter tunnels for rail - the same size as the CRL tunnels - have been estimated to cost up to $1.5 billion.
Green Party transport spokesperson Julie Anne Genter said Auckland can't stop now because the city's huge population growth meant the Government needed to urgently prioritise extending the rail and bus networks.
"Now that the CRL is under construction, the Government must start planning for rail to the airport and across the harbour, to help the growing number of people living on the North Shore get into the city.
"The CRL is just the first step in the development of a high quality commuter rail and public transport system in Auckland, but it's a big step because it shows what's possible," said Ms Genter.
Transport lobby group Generation Zero said the long planned project was finally underway thanks to the tireless effort of Auckland Transport and Auckland Council who fought for the CRL for years.
"The CRL is the heart of a much needed rapid transport network in Auckland. But it can't stop here. We need rail to the North Shore, rail to the airport, light rail in the isthmus, there is plenty left to do."
Transport Minister Simon Bridges said the project will be a catalyst for other big development projects around the Auckland CBD.
He said today's ground-breaking and official start of construction of the City Rail Link has been long-awaited and is something that will help reduce Auckland's transport issues.
"With Auckland's population predicted to grow by more than 700,000 people over the next 30 years, the CRL will play an important role in getting people in and out of the city with ease," Mr Bridges said.
"It will double the capacity of Auckland's rail network, provide two new stations in the central city and see travel times for commuters reduce significantly."
