Residents near The Ridge in Hastings are being advised to keep windows and doors closed as a precaution following an earlier fire at a derelict care home.
About 40 firefighters were called out to the Mount Denys care home just before 05:00 BST.
There were no reports of any casualties.
An investigation into the cause of the blaze is under way.
It was the latest in a number of fires at the site in recent weeks.
Southern Water has warned that water pressure and supplies in the area could still be affected because firefighters were using hydrants.