A writer who was at London's Apollo Theatre when the ceiling collapsed said he saw "a lot of kids traumatised, covered in dust and blood being comforted by parents".
The Independent features writer Simon Usborne told Daybreak: "There were screams, it was immediately clear something serious had happened.
"Nobody told anyone to move - everybody rose immediately and ran to the nearest exit".
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Chelsea had planned an open top bus tour to show off the Premier League trophy and hope to add the FA Cup in Saturday's final with Arsenal.
Schoolchildren put on a spontaneous show of unity in the wake of the Manchester Arena attack.
The Islamic centre where the Manchester suicide bomber is thought to have prayed says the attack "has no place in Islam or any religion".