An internal systems failure has shut a secondary school serving more than 2,000 pupils.
Stanground Academy in Peterborough sent out a letter to parents on Monday informing them about the school's closure on Tuesday.
The academy called it "an unprecedented failure by an external supplier to the [academy] trust".
"We cannot provide a safe system of care for pupils and therefore will remain shut," it said.
Stanground Academy is run by the Greenwood Academies Trust for children aged 11-19.
In the letter, the school also "apologised for the inconvenience to the parents".
The academy said: "Our internet provider has impacted on the critical systems including no fire alarm. or no registration system for students or staff.
"It would also mean no access to emergency contact details.
"We will continue to work with the supplier to find a solution for this failure and ensure that the situation is resolved for Wednesday."
The academy thanked parents for their patience and said it would continue communicating with them via the school website, its Facebook page and Group Call via parents' mobile phones.