The MetService has issued a heavy rain warning for the Bay of Plenty with up to 100mm of rain expected over the next 12 hour period.

A complex trough of low pressure over the North Island is expected to move slowly eastwards today, before stalling near East Cape early Monday while a ridge builds over the South Island.

Heavy southeasterly rain is expected to continue about Hawkes Bay and Gisborne south of about Tolaga Bay through to late Monday afternoon, and 250mm could accumulate about the hills and ranges.

The MesService says in addition, 100mm could fall about parts of the Bay of Plenty in a 12 hour period.

Rain currently falling over Hawkes Bay and Taihape is expected to turn to snow above 800m tonight, and 25cm could accumulate in some places through to late Monday afternoon.

People are advised heavy rain has the potential to cause rivers and streams to rise rapidly, with surface flooding possible in low lying areas.

Also, heavy snow can cause significant disruption to traffic and stress to young livestock the MetService says.