Fire crews are battling a blaze at Baines School in Poulton.
Six fire engines are at the scene in High Cross Road, where a fire has broken out in the sports hall.
The fire service said children and teachers are safe and no injuries have been reported.
The blaze, which reportedly involved gym equipment, was quickly contained and brought under control by firefighters.
The school said an evacuation was not necessary and it will close at the normal time today.
But parents are advised that High Cross Road remains closed and there will be limited access at the school pick-up time.
Blackpool Transport said its Service 2 bus from Poulton will use Longhouse Lane and return via Garstang Road.
A spokesman for Baines School said: "You may have heard that we have the Fire Service on site dealing with an incident.
"We have no concerns for the safety of students and we would appreciate everyone keeping our phone lines clear.
"We will provide an update to our school community later today."