Two hundred people were advised to evacuate from their homes in Helston overnight after flooding in the town.
A severe flood warning has been issued after the River Cober rose and burst its banks during overnight rain.
People living in St Johns Road, St Johns Close, Coronation Park and the Loe Pool area were woken and offered shelter at an emergency rest centre at Epworth Hall.
The bridge over the river at St Johns has been closed to traffic due to the force of water.
With more heavy rain forecast for this morning after nearly two inches fell on the county overnight, further problems are expected to develop through the day.
The A39 at Stickenbridge/Perranarworthal and the A39 at the Glyn Valley are currently closed and surface water flooding is affecting a number of roads across Cornwall.
According to Cornwall Council, there are reports of flooding at areas including Durgan, Hayle, Helston, Mousehole, Penryn, Penzance, Probus, St Erth, St Just, and Godolphin Cross.
A council spokesman said: "Agencies are asking people to follow the advice on dealing with the potential severe weather, and are warning people not to drive through flood water.
"Over the past few days a number of people had to be rescued from their cars after driving though floodwater.
"Driving through flood water can also create waves which can then affect properties. As today is expected to be a busy day as people do their Christmas shopping, members of the public are also being advised to delay travelling until the day light hours if possible and exercise extreme caution on the roads."
Local communities are also encouraged to check with vulnerable neighbours in case they need help with obtaining flood protection materials.
Sandbags can be obtained from builders merchants, DIY and hardware stores. Anyone who is unsure if their property is at risk can check on the environment agency website www.environment-agency.gov.uk or call the floodline on 0845 988 1188.
For further advice on preparing for flooding visit the environment agency website www.environment-agency.gov.uk or the Cornwall Council website at www.cornwall.gov.uk/flooding
For regular updates follow @CornwallCouncil, @DC_Police and @EnvAgencySW or hashtag #ccfloods on Twitter To report flooding incidents which are not posing a risk to life, contact 0300 1234 100.