A boy is critically ill after suffering burns when a makeshift aerosol blowtorch caused an explosion.
The 13-year-old boy from Leeds was engulfed in flames as he played with a friend on waste ground in Meanwood Road on Sunday evening.
The explosion is thought to have been caused when a jet from an aerosol was directed on to another can containing flammable liquid.
The boy is being treated at Manchester Royal Infirmary.
Two police officers, who were on patrol in the area, saw the incident and went to the teenager's aid.
A spokesman for West Yorkshire Police said: "At 9.20pm on Sunday officers on patrol in Meanwood Road noticed two youths on nearby waste ground and then saw an explosion which resulted in one youth being engulfed in flames."
The boy was initially taken to Leeds General Infirmary and later transferred to the specialist children's burns unit at Manchester.
The police spokesman said the boy's friend, also 13, was not injured.
He added: "Inquiries so far indicate this was a tragic accident."