The Fire Service says it has been fielding dozens of calls from people in South Canterbury and Otago who have reported flooding problems.
MetService has forecast up to 100mm of rain for the area until Wednesday.
The Fire Service says by late on Tuesday night, it had received about 35 calls from people in Temuka, Oamaru and Dunedin.
A spokesperson says crews have been out to people's homes that have flooded and roads that are impassable.
Earlier, the Otago Regional Council issued a flood warning for the Pomahaka River in South Otago.
High flows are expected in Dunedin streams and all rivers north of Dunedin, as well as in the Taieri and Manuherikia rivers.
