Roads are closed and dozens of households are isolated in parts of North Otago by three weeks of constant rain that has brought flooding and slips.
Moderate to heavy rain is forecast to hit Otago and parts of South Canterbury overnight but it should ease on Wednesday.
MetService forecaster, Gerard Barrow, says about 40mm of rain will fall in parts of Otago and 30 mm in southern Canterbury until 6am Wednesday.
About 40 roads in north Otago are closed Tuesday night by floods and slips.
More than 50mm of rain has fallen in parts of North and coastal Otago on already waterlogged ground.
Waitaki District Council is advising caution on dozens of roads and has had teams out and about assessing the flooding on Tuesday.
The emergency services manager at the council, Chris Raine, says it is trying to work out how many households are cut off because of the closed roads but the best estimate is dozens.
Teams have been out door knocking to check on people but the conditions are so dangerous now that this activity has been stopped.
Mr Raine says if locals are isolated and need help, ring the council.
Mr Barrow says by Wednesday afternoon, rain in Canterbury and North Otago should ease, but says some light rain is possible in other parts of Otago.
In Christchurch, the city council says there is minor flooding in parts and minor slips on the Banks Peninsula.
Canterbury Regional Council says while some flooding could occur on roads and paddocks in South Canterbury, it is likely rivers will cope.