Power is slowly returning to downtown Auckland after an outage crippled the centre city and forced the closure of Britomart rail station.

Vector had earlier warned that the CBD and Parnell could remain "without power for some time" after the lunchtime outage struck at about 12.30pm.

The cause is still being investigated.

We can now confirm that power to the remaining parts of Parnell, has also now been restored. The cause is still being investigated.

— Vector Ltd (@Vectorltd) January 23, 2020

The "chaotic" power cut spanned the city centre, and parts of Newmarket and Parnell.

Vector said just before 2pm that power had been restored to the CBD and Parnell.

Britomart train station was forced to close and multiple traffic lights stopped working.

Power was restored to Britomart soon after 1.30pm - but it could take until 3pm for normal services to resume.

Vector said at 1.45pm that power had been restored to the CBD, though parts of Parnell were not fixed.

Earlier, the company confirmed the outage had affected Quay St, parts of Auckland's CBD and parts of Parnell.

"Vector's electricity operations centre is remotely redirecting power flows to as many affected customers as possible, and our crews are currently working on the fault," the company said.

"Customers in these areas should prepare to be without power for some time while we respond to the outage. The objective of our crews is to do this as quickly as possible while ensuring the safety of our crews and the public."

Rail services had to end at Newmarket for the Southern, Western and Onehunga lines, and at Orakei for the Eastern line.

Power was knocked out at Better Burger in Auckland's CDB, near Britomart. Photo / RNZ