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A sea of red smoke covered a town centre square tonight as a flare was set off.
It came as fans digested England's 2-1 defeat against Croatia.
Police had already been stationed around Maidstone after two flares were earlier released. One came after Kieran Trippier's early goal.
But while much of the crowd stuck to chanting, someone decided to send the missile into the crowd in Jubilee Square, smothering others in the smoke.
Police patrols had been stepped up as hundreds of fans packed out bars on an historic night for the nation.