Major flooding across the Otago region with heavy rain looking set to continue throughout the night

Councils and Civil Defence Services are on full alert - doing everything from handing out sandbags to pumping water off the runway at the Dunedin airport.

Civil Defence Controller Sandy Graham says the Taieri River has burst its banks and they're deciding whether to open the spillway gate.

She says some homes may need to be evacuated.

But Niwa forecaster Ben Noll says things should improve soon.

He says the rain is expected to move out of Otago and Canterbury before tomorrow.