An air ambulance is also attending the incident on Barking Road in east London.
A video shared on Twitter shows a number of police and ambulance vehicles at the scene.
Crowds of people can also be seen gathering.
One person tweeted: “Trying to get through Canning Town and ambulances, police and air ambulance blocking Barking road.
“I don’t know what has happened but pray for whoever is hurt.
“Having to now comfort kids who feel scared.”
Express.co.uk has contacted the Metropolitan Police for further information.
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