West Coast Police say a local woman is lucky to be alive - after crashing her car into a river and being swept out to sea

The 41-year-old was found around 7.30 this morning, after a dramatic search and rescue mission along the Arahura River overnight.

Her six-year-old son was able to get out of the crashed car and walk nearly two kilometres to State Highway 6 where he was found just before 2 this morning.

He told Police that his mother was in the water and he couldn't get her out.

The search involved a range of organisations, as well as members of the jet boating community and a helicopter with thermal imaging equipment

The woman is currently being treated for hypothermia in hospital in Greymouth.