Auckland's City Rail Link is facing ballooning costs and could miss the 2024 completion date

The 4.4 billion dollar project has endured 205 days of Covid-19 lockdowns and restricted working conditions.

City Rail Link chief executive Dr Sean Sweeney says the biggest challenge is Covid and its very long shadow.

He says they're working out how significant the impact on the City Rail Link will be ... with the aim of having a clear picture by the end of the year.

As well as the impact on work sites, the project is having to manage rising costs for materials and supply chain issues ... and getting skilled workers from overseas.

In early 2019 the cost shot up by one billion dollars ... to 4.4 billion.