Weather: Canterbury homes without power, roads flooded as red-alert level rain sets in

Some Christchurch homes woke without power on Sunday morning as a red-alert level deluge set in overnight.

MetService earlier this week issued what was only its second-ever "red warning", as Cantabrians prepared for a huge amount of rain to be dumped.

Central Canterbury lines company Orion says as of 6:10am on Sunday, 241 homes in Christchurch were without power but that has since been restored. Another 80 remain without power in the Selwyn District.

A police spokesperson told Newshub there's been flooding in several Christchurch suburbs overnight including on Belfast's Main North Rd and Aranui's Anzac Dr, where traffic management remains in place.

The NZ Transport Agency (NZTA) says State Highway 73 between Springfield and Castle Hill is closed due to slips and flooding.

"Please delay your journey between Canterbury and the West Coast, as there is only a long detour available via SH1 and SH7," a Waka Kotahi NZTA spokesperson said on Twitter.

MetService meteorologist Tom Adams says another two days of persistent rain is expected.

"It's just going to be rain building and building - particularly up in the headwaters, in the Canterbury High Country but also some lower down," he told Newshub. "That's going to mean that rivers are going to rise."

Adams warned roads could be flooded or impassable as a result of the rain. The red warning covers a large chunk of the Canterbury region south of Amberley.

"In addition to rain which has already accumulated, expect 200 to 300mm of rain about the Canterbury High Country and foothills," MetService warns. "With 100 to 140mm of rain farther east about the plains and coast."

NIWA said on Saturday gusty winds were also expected.

"From tonight through early Monday, easterly winds may gust near or over 70 km/h at times," a post on the forecaster's Twitter page said, adding the weather may down trees and cause power cuts. 

Further north, a road in Gisborne has been closed overnight by a large slip.

Motorists hoping to use Tinoroto Rd are being urged to use an alternative route between Gisborne and Wairoa - such as State Highway 2.

Police said contractors are set to reassess the situation later on Sunday morning.