More than 500 pupils were given the day off after a gas leak at their school.
The caretaker detected the leak at Eastbury Primary in Dawson Avenue, Barking, after 5am on Monday.
School staff used Facebook to advise parents the 640-place primary would be closed that day.
Engineers were called in and the school reopened this morning.
Barking and Dagenham Council said the gas escape came from an “intake room” which has equipment such as boilers, but stressed the school’s gas systems were in good working order.
A spokesman said Eastbury had been closed “as a precaution” and added: “The supply to the kitchen has been restored and the school will now be open as usual.”
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