Canterbury in for a drenching as rain system moves south

Heavy rain that drenched parts of the country overnight has headed south to Canterbury, where Christchurch City Council has pumps on standby in case of flooding.

Canterbury Plains north of Ashburton, including the foothills and Christchurch, are under a heavy rain warning.

Warnings are also in place for Coromandel, Bay of Plenty, Gisborne, Tasman (about and west of Motueka) and eastern Marlborough south of Blenheim.

Police are asking motorists to avoid or delay travel between Blenheim and Kaikōura, with multiple slips on State Highway 1 causing blockages.

A fallen tree closed SH 2 north of Tangoio Settlement Rd in Hawke's Bay.

Overnight, strong winds and heavy rain caused about 37 power outages across the Auckland region as branches, debris and trees fell onto power lines.

Rain eased early morning from Northern Coromandel, but remained steady near Gisborne. There were no reports of flooding or damage overnight, but Tolaga Bay Civil Defence Manager Greg Shelton said teams were still on standby.

Pumps on standby in case of Christchurch flooding

Christchurch residents are being warned of hammering rain as up to three times the city's average December rainfall is forecast to fall over a 24-hour period.

MetService meteorologist Angus Hines said surface flooding was likely.

"Just over a 24-hour period between 100mm and 150mm of rain is expected to pile up to parts of Canterbury and Marlborough," he said.

"That is a lot for that part of the country. Take Christchurch for example, their average December rainfall is about 47 millimetres on average across the entire map so there's a chance that Christchurch could well and truly exceed that in a day."

Christchurch City Council had pumps on standby as surface flooding was expected in low-lying areas of the city.

But it warned residents in the port suburb of Lyttelton they would see stormwater flows on their streets as contractors repaired a collapsed and blocked stormwater drain.

Sandbags were being deployed around some homes there and traffic measures will be in force.

Deputy mayor Andrew Turner said the council was taking all precautions it could to ensure the stormwater was diverted and nearby properties were protected.

Stormwater upstream of the blocked section of pipe will be pumped away, diverted down St Davids, Oxford and Exeter streets.

Lyttelton residents living on Oxford Street, downstream of Rippon Street, were asked not to park their cars on the road.

Motorists were advised to take care on the roads and drive slowly through surface flooding.

"Also, try and avoid walking or biking through surface flooding as there is a chance it could be contaminated with wastewater," the council's head of three waters and waste, Helen Beaumont said.

Waimakariri District Council said contractors had cleared drains as a precaution ahead of heavy rainfall.