Robertson Elementary School is closed Sept. 1, after a fire broke out inside the building Monday night, displacing students across the south Tulsa campus.

Tulsa firefighters responded to the school near 51st Street and Union Avenue around 10 p.m. Aug. 31, after reports of a fire inside the building, News On 6 reported. When crews arrived, they found smoke in one classroom and the sprinkler system already activated.

One classroom sustained fire damage. Several other classrooms had smoke and water damage from the sprinklers, according to investigators cited by News On 6.

Janitorial staff were inside the school at the time of the fire but no one was injured, officials said. No students or staff were present.

Tulsa Public Schools announced the closure early Tuesday morning, KJRH reported. The district said in a statement that the fire was isolated to one classroom and quickly extinguished. The Tulsa Fire Department and Campus Police cleared the building after the blaze.

The district said its teams would spend Tuesday cleaning the building and working to prepare it for reopening as soon as possible, according to KJRH.

Cause unknown

The Tulsa Fire Department has not determined what started the fire. An official with Tulsa Public Schools told KTUL the source of the blaze is unknown. No arson or accidental determination has been released.

A decision on whether Robertson Elementary will reopen Sept. 2 was expected later Tuesday afternoon, according to KTUL.

The number of students affected by the closure was not immediately available from the district.