Power has been restored after a "major" hour-long outage hit Christchurch Hospital earlier tonight.

The outage "affected all systems including power, IT and phones", the hospital said in a statement.

"Unless it's an emergency, please seek alternative care," it added.

A statement on the Te Whatu Ora ‐ Waitaha Canterbury Facebook page at about 10.35pm confirmed power had been restored.

"The Waipapa acute services building is receiving power from its on-site generators, while the Parkside and Riverside buildings are back on mains power," the statement read, adding the outage "left some areas in total darkness earlier this evening".

"We will be reviewing why the generators didn't automatically connect to the hospital's systems when the power failed.

"Thankfully all 478 patients in our care, including 96 in ED at the time the power went out are safe."