Christchurch's state of emergency will stay in place for another day.

The city is in clean-up mode after the big weekend's massive dumping of rain. Parts of the city remain underwater, after the Heathcote River burst its banks on Saturday.

Mayor Lianne Dalziel said dozens of city properties are affected and some will need a lot of clean up.

She said water levels are still high and cordons have to stay where they are.

"We'll review that tomorrow, so we intend to leave that state of emergency in place. We're still getting high tides."

Meanwhile, Civil Defence Controller Anne Columbus said they've yet to ascertain just how many people are affected.

"That picture's still emerging, given we know we have a couple of dozen homes flooded, but we have our response and evaluation teams back out on the scene today."

She said anyone re-entering their home should be extremely careful, particularly where there's been flooding, people have to be careful too, and think about the electricity.

Wastewater overflows in Christchurch and Banks Peninsula have stopped, so people no longer need to conserve water.

Meanwhile, the state of emergency in Dunedin could lift in the coming hours.

But parts of the Waitaki District may still need to come under one because of what's being called enormous damage.

Elsewhere in the region, farmers have been taken aback by just how quickly things turned bad in the South Island deluge.

Oamaru had three times its average rain for July dumped in just one day.

Federated Farmers South Canterbury president Mark Adams said almost every farm's been affected somehow, with the soils being saturated.

"Whilst we had 90 mm (of rain), we were amazed at how quickly the rivers came up for what we thought was just a simply above average winter rain."

In his area, he believes it was a one in 10 year event.

He said most farms were affected and it is farming infrastructure like tracks, fences, flood-gates and culverts that bear the brunt.

Mr Adams said it's too hard to say how long the clean-ups will take, and how much it'll all cost.