Three people are injured and are receiving treatment after an incident at Ysgol Dyffryn Aman in south-west Wales.
After being locked down in classrooms since the incident at 11:15, pupils were allowed to leave the school at 15:20.
School governor Karen Davies tells Wales Online she believes that two members of staff were injured in a stabbing. Police and air ambulance helicopters were sent to the school in Ammanford in Carmarthenshire.
Police urged people not to share footage of the incident on social media or speculate about what happened.
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