A major mop-up operation has been launched in North Canterbury after yesterday's torrential downpour caused widespread flooding.

The deluge has since eased enough for most of the surface flooding around the worst-hit towns of Rangiora, Oxford and Kaiapoi to subside today.

State Highway 1, between Waikuku and Amberley, reopened this morning.

But the New Zealand Transport Agency has urged for extreme caution when driving from Christchurch to Picton today with some surface flooding still remaining and conditions hazardous in areas.


"Motorists are advised to lower their speed and increase their following distances to reduce any risk of a crash," said NZTA performance manager Pete Connors.

Waimakariri District Council's emergency operations centre was in operation through the night last night dealing with problems arising from yesterday's flooding around the district.

A boil water notice for residents connected to Oxford's rural no. 2 water supply was put into effect late yesterday.

The notice is still in effect and residents are being advised to boil all drinking water until further notice.

A number of roads have suffered damage during the flooding and people are advised to take extreme care when driving and particularly be on the lookout for road damage such as potholes and other road damage.

Council staff and contractors were out in force this morning checking flood damage, drainage and roads before making assessments as to the extent of repair work necessary.

"Some of those repairs can be immediate, but it is very likely that there will be issues that will need addressing over the longer term as a result of flood damage," said the district council's emergency operations centre controller, Nick Harrison.

The rain storm hit at a time when the region's water table is extremely high after the last two months of heavy rain.


Mr Harrison said Waimakariri has already this year exceeded its average annual rainfall.

"This not only exacerbates current issues but also can create new issues ? the extent of which is uncertain at this stage," he said.

"Once we've had a chance to examine the extent of damage and formulate a recovery approach based on that, the recovery task can be set in motion."

The emergency operations centre is still operating at this stage.

A decision as to whether to continue it at full strength or on a reduced basis will be made later today, the council says.

Waimakariri Civil Defence emergency management staff worked through the night to answer calls from residents.

Most of the flood waters have receded significantly today.

Now, Civil Defence staff are knocking on doors to check that residents in the worst-hit areas are coping.