A school in London faces an uncertain future after a chalk mine was found underneath it. Geological surveys have found an "unacceptable risk" that the ground below the Pinner Wood School, in Pinner, north-west London, could become unstable, Harrow Council said.
Pupils of the primary school have been told they will not be able to return to the site until further notice.
But it is also possible they will never be able to return to their school.
Harrow Council said classes would relocate to other educational settings for the summer term while more tests were carried out to assess the site's condition and safety.
Laser imaging scans took place to map the uncharted an unknown tunnels under the school and revealed that in several areas, the roof has collapsed.
Further surveys could take months to complete and it is possible that the school site may be deemed so unsafe that it may never be able to open again.
Head Deb Spruce said: "This is a huge and sudden shock to all of us. We absolutely need to leave this site until it is made safe.
"Our school is blessed with exceptional staff and governors and a wonderful parent group. I'm certain we will all rise to this challenge and show that our Outstanding school is united by much more than just our buildings."
During the summer holidays of 2015, a hole unexpectedly opened in the tarmac of the staff car park at the school. It was roughly 3 metres wide and 1 metre deep.
The council and school made the area safe and commissioned specialist geotechnical engineers, structural engineers, environmental engineers, surveyors, geophysicists and health and safety professionals to analyse the causes of the hole. That led to the discovery of a former shaft.
Almost two years later the full extent of the dangers were revealed and the surveys found that the roof collapses were likely to migrate through the ground and open new surface holes under or near the school at some point in the future.
Cllr Sachin Shah, Leader of Harrow Council said: "With the evidence we have discovered in the past few days, we are certain that this is the right decision.
"We would like to stress that the imminent risk to the school buildings is believed to be small. However, the council would never ask or permit any school to operate when there is a known risk, however small, to the safety of the site or the staff and children within it."
Dr Clive Edmonds, partner at Peter Brett Associates, which carried out the geotechnical surveys, said it was likely that the mines dated from the early 1800s.
"As is common for chalk mines of this age there are no mine abandonment plans and the mine workings are in a state of breakdown, as confirmed by the laser survey, posing a hazard to surface stability."