An extra four fire engines were called in at around 6pm to help tackle the blaze at John Ray Infant School in Braintree.
Thirty firefighters are tackling a blaze at a school in Essex.
Seven fire engines have been at John Ray Infants School on Notley Road in Braintree since about 4.30pm this afternoon.
There aren't thought to be any casualties.
The cause of the fire isn't clear at this stage.