Twelve children and one adult were taken to hospital after a ceiling collapsed at Rosemead Preparatory School in Dulwich on Monday morning.
The London Ambulance Service said it had treated a further 16 people after being made aware of the incident at 9.24am on Monday.
Rosemead Primary School said it is “working closely with the authorities” to understand what caused a ceiling to collapse in one of its Year 3 classrooms.
A statement from the school said: “This morning in one of our Year 3 classrooms, a ceiling collapsed resulting in the attendance of the emergency services.
“Some injuries were sustained and some of those involved have been taken to hospital, and we are working with our students and families to support them.
“We are working closely with the authorities to understand the cause of the incident and we will provide more information as soon as we can.
“Parents and families can be reassured that the school day is continuing as usual today for the rest of the school.”
Emergency services have left the scene in Thurlow Park Road and roads have re-opened.
It said the incident was over for crews by 11.50am.
They added: “All other children and staff were safely evacuated from the building. Firefighters carried out a systematic search of the building and confirmed with the school that all children and staff were accounted for.
“A specialist USAR (Urban Search and Rescue) team and equipment were also used to confirm the building was at no further risk of collapse.”
A London Ambulance Service spokesperson said: "We were called at 9.24am today (November 15) to reports of an incident at Rosemead Preparatory School, SE21.
“We sent a number of resources to the scene, including ambulance crews, medics in cars, advanced paramedics, incident response officers, emergency planning resilience officers, our hazardous area response team, and a command support vehicle.
“We treated 16 people at the scene, and took 12 children and one adult to hospital.”
Rosemead Preparatory School teaches children from pre-nursey to year six.
Labour’s Helen Hayes, the MP for Dulwich and West Norwood, said: “Very concerned to hear of the collapse of a ceiling at Rosemead School this morning.
“My thoughts are with the children, staff and parents. I hope no-one is seriously injured.
“I’ve contacted the school to offer my support. My thanks to the emergency services who attended the scene.”
A Metropolitan Police spokesman said that “all children and staff have been accounted for and the school is currently in the process of contacting parents.”
They added: “We await an update on assessment of any injuries”.
Many people have sent their well wishes to the children involved on social media, with one person commenting: “Hope there all got out with minor injuries”.
Another said: “Wish you all quick recovery”.