A fundraising appeal has begun to repair a church in the village of Merstham, parts of which were built in the 13th Century.
Villagers said they need to raise about £300,000 to protect the tower of St Katharine's Church in Church Hill.
An architect's inspection found the shell coating protecting the stonework from erosion has begun to drop off.
Church leaders said if the work was not carried out on the Grade II listed building, the tower may become unsafe.
Churchwarden Gill Buchanan said: "There's been a church on the site for hundreds of years. Most of it was built in 1220.
"It's very important to the community and lots of people think about it being their church.
"It's crumbling away and we need to preserve it for future generations.
"We need to do the work in the next year or so otherwise it will get so bad it may become unsafe."
Ms Buchanan said more than £100,000 has been raised with support from English Heritage and the Surrey Churches Preservation Trust.