Four children are being treated in hospital after a firework exploded in their faces.
Emergency services, including two air ambulances, were called to Nelson, Lancashire, shortly before midday on Thursday.
One child was taken by helicopter to Alder Hey Children's Hospital, Merseyside, while the other three were sent to the Royal Manchester Children's Hospital, one by air ambulance.
No information on their conditions has been released.
Police said the youngsters, aged between nine and 12, were found in the street by community support officers who came across the incident while they were on patrol.
Sergeant Shaun Pearson, posting on Lancashire Police's Nelson, Brierfield and Barrowford Facebook page, issued a stark warning about the dangers of fireworks.
"Air ambulances have just taken off from Lidl car park and Walverden Park to take two children injured by fireworks to hospital," he said.
"Another two children transported by road ambulance. The children aged 9-12 years were messing about with fireworks in the Albert St area when one has gone off in their faces.
"I don't need to post pictures on here of crying children with blood and burns on their faces. PLEASE DON'T MESS ABOUT WITH FIREWORKS."
A spokeswoman for North West Ambulance Service confirmed crews were called to the scene at 11.53am.
Police across the UK have issued warnings to youngsters about the dangers of fireworks in the run-up to Bonfire Night on Saturday.
On Halloween night, police were attacked with fireworks in two separate incidents in Tottenham, north London, and Birmingham.