People have been rescued from their homes after heavy rain and gale-force winds led to heavy flooding.
Devon and Cornwall police said it was dealing with a "major flooding incident" after heavy rain overnight around St Austell, Cornwall.
There have been no reports of serious injuries but people are being advised not to travel.
A Devon and Cornwall Police spokesman said: "Due to heavy rainfall overnight, parts of mid and north Cornwall have been affected by serious flooding.
"Areas of St Austell and St Blazey are impassable and people have been trapped in their cars and homes.
David Cameron told MPs during Commons question time: "There was a very difficult night in central and south east Cornwall."
The Prime Minister said: "I think the emergency services, the police, the coastguard, the fire services, fire and rescue - they've been working round the clock and they've done a fantastic job."