Police are investigating after three people were taken ill, after coming into contact with a package in Truro.
Cornwall Fire and Rescue's hazard materials team as well as police and ambulance services are all on the scene at Penhalls Way, Playing Place.
No other properties are believed to be affected.
A campaign has begun urging motorists not to risk their lives by driving through flood water.
It's called 'Turn Around, Don't Drown' and is run by Cornwall Fire & Rescue Service.
Crews have been demonstrating the dangers involved in driving through water that's too deep.
You can see footage of Cornwall Fire Service re-enactment of a water rescue below:
A campaign urging motorists not to risk their lives by driving through flood water is launched today.
Called 'Turn Around, Don't Drown', Cornwall Fire Service will be demontrating the risks involved in taking a chance with water that could potentially be much deeper than drivers suspect.
Cornwall Fire and Rescue Service is set to share its emergency call centre with its counterparts in North Yorkshire under a scheme being considered by Cornwall Council.
Both services would retain their own control rooms, but under the new arrangement Cornwall’s would receive calls on behalf of North Yorkshire during busy periods. Similarly, North Yorkshire’s Control Room will be able to provide the same service for Cornwall during busy periods.
Cornwall Council says the main cause of busy periods for both services is severe weather. This new arrangement increases capacity to deal with higher call volumes, as Cornwall and North Yorkshire tend not to be affected by severe weather at the same time.
The council says some night-time control rooms will go, but the number of staff on duty will remain the same as they will be utilised for wider roles to assist other Council departments outside normal office hours.
Cornwall Council cabinet member for homes and communities Geoff Brown said; “This project will provide a better service to people calling for the fire and rescue service in each area and will save taxpayers money.”
Ten thousand householders in Cornwall are getting letters today urging them to do more to protect their homes from flooding.
But the warning is going out that it isn't just residents that need to be prepared. Fire crews in Cornwall have seen their role increasingly change from fighting fires, to tackling floods. New skills, such as river rescue are now an essential part of the job.