Mayor Helen Lash has declared a local state of emergency for the southern ward of Westland District.

It comes as parts of the West Coast experience their wettest night in decades as emergency managers continue to closely monitor the situation.

West Coast Emergency Management said the declaration was made "as extensive flooding causes significant problems across the district, including evacuations, road closures and landslips in the South Westland area.

"This declaration provides for controllers to direct and coordinate personnel, material and other resources made available and provides access to extraordinary powers to deliver an effective and timely response to an emergency.

"Members of the public are reminded to prepare getaway bags in preparation for potential evacuations.

"If anyone is feeling unsafe, please self-evacuate to friends or family on higher ground or call 111."

Orange level rain warnings are in place for Westland until at least this afternoon, with a small chance warnings could escalate to red.

West Coast Civil Defence has partially activated its emergency operations centre, with emergency managers meeting later on Saturday morning.

Claire Brown from West Coast Emergency Management has asked people to avoid travel, particularly in the south of the Westlands area, with some road closures in place.

These include State Highway 6 from Fox Glacier to Haast, due to a slip, and Ross to Fox Glacier because of flooding and slips.

About 350 millimetres of rain had fallen across the coast in the 24 hours to 7am.

Franz Josef experienced its wettest 24 hours in 45 years.

Emergency Management minister Mark Mitchell earlier said Westland residents should stay off the roads as heavy rain continues to fall.

Mitchell said Emergency Management officials and the community are well prepared, but they need to stay vigilant, and stay off the roads if they can.