A large downpour of rain's expected to strike the bottom of the South Island tonight

MetService has issued an Orange Heavy Rain Warning from 5 pm - for south of Dunedin City and the area around the Otago Coast.

It's expected to peak between five and eight millimetres overnight.

MetService advises people to clear drains and gutters in preparation - and avoid low lying areas.

Surface flooding, slips and difficult driving conditions are possible.