Calls were made to the emergency services on Friday reporting that a person had been found unconscious and not breathing in a street in Blackburn.
As the ambulance crews arrived, they were attacked by juveniles who threw fireworks, resulting in the crews having to retreat to their vehicle.
When police were called to assist, they were also attacked by the group with fireworks, with the whole incident, in the Audley area of the town, filmed by the teenagers using mobile phones.
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It is believed the 'unconscious person' reported was a hoax call to lure emergency services to the area to be attacked.
Police have condemned the actions of the group and are now asking parents to speak with their children if they suspect they may have been involved in an event that could have prevented the crews from doing their jobs.
A spokesman for Lancashire Police said: "To put members of the emergency services at risk and prevent them trying to save someone's life is completely unacceptable.
"If you suspect your child to have been involved we would ask you to speak to them because next time it could be someone you know needing help."