MetService expects 80 to 120mm of rain in coastal Otago by Monday morning.

A heavy rain warning has been issued for coastal Otago - with a chance of it turning into a red warning - as several other parts of the South Island brace for heavy snow and rain.

MetService expects 80 to 120mm of rain in coastal Otago by Monday morning.

Heavy rainfall has arrived in Dunedin earlier than expected and is forecast to continue overnight, with surface flooding and some land instability reported.