Police, ambulance and fire engines rushed "a chemical incident" outside a school this afternoon where children were heard playing.
Princess May Primary School was evacuated over leak fears with multiple people treated after the mystery smell was reported.
Paramedics are treat multiple patients after being called out to Stoke Newington in Hackney, north-east London.
A spokesperson for the London Fire Brigade confirmed that the incident is now over, with no elevated chemical readings taken.
One eye-witness told the Mirror that - despite it coming in the school holiday - they heard some children outside playing.
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"Firefighters attended a suspected chemical incident on Barretts Grove in Hackney," an earlier London Fire Brigade statement read.
"A number of people complained of smelling chemicals and fire crews evacuated around 30 people from the school.
"Firefighters are carrying out a sweep of the building to try and detect any raised levels of chemicals."
Emergency services were called to attend the scene just before 11.30am this morning.
A London Ambulance Service spokesperson that there is no carbon monoxide present in the school after a reading was taken.
They said: "We were called at 11.23am today to reports of an incident at Princess May Primary School, Hackney.
"We sent a number of resources to the scene, including two ambulance crews, a medic in a fast response car, an incident response officer and members of our hazardous area response team.
"We are assessing a number of people at the scene.
"The incident is ongoing and we are working with our emergency service colleagues."
Video footage circulating online have shown multiple police, ambulance and fire service vehicles on the scene outside Princess May Primary School, where children are thankfully on their summer break.
One worried eye-witness told the Mirror: "Well obviously school isn’t running fully because of the school holidays but I did hear some kids playing outside in the nursery bit of the school. I’m an ex pupil."