Auckland’s new City Rail Link network faced delays and cancellations on its first day of service due to a fire at Waitematā station.

A small fire started by an electrical cable near the ceiling forced the evacuation of the central Auckland station causing disruption to all lines on Sunday morning, but rail bosses said the fire proved the emergency systems worked exactly as intended.

"How disappointing is it, though, to have something like this on the very first day," Auckland Transport chief executive Stacey van der Putten said.

"These things happen. It's an active railway. You can't predict these things. What we were really impressed with was how the system responded, and it responded quickly."

By 8.55am passengers were able to stop at Waitematā Station.

Van der Putten said there had been no other hiccups across the network.

 The first train left at 4.57am from Ōtāhuhu into Auckland.

The $5.5 billion underground rail system - New Zealand's first - is also the country's largest transportation infrastructure project and has taken a decade to build.

The massive project that adds two 3.45km tunnels deep underground that will link Auckland's existing rail lines into one network and allow the rail system to almost quadruple its capacity.

It also includes two huge new train stations downtown - Te Waihorotiu and Karanga-a-Hape - and renovations to the Maungawhau and Waitematā stations.