A 15-year-old boy was seriously hurt when a banger exploded in his hand and a 12-year-old boy suffered superficial burns to his hand after being scorched by the same type of firework.
The teenager was injured during the incident in Motherwell, North Lanarkshire, at about 5.20pm yesterday.
He was taken by ambulance to Wishaw General Hospital but was later transferred to Glasgow Royal Infirmary, where his condition is described as stable.
Police said his hand was seriously injured.
Earlier today, a 12-year-old boy suffered superficial burns to his hand after being scorched by the same type of firework.
He was treated at Wishaw General Hospital following the incident in Wrangholm Drive, Carfin, also North Lanarkshire, at 2.30pm, and was later released.
Strathclyde Police said up to 1,000 bangers, which consist of a rolled up paper tube filled with gunpowder and a fuse at the top, were being stored in a shed behind houses in Blackmoore Place, New Stevenston, North Lanarkshire.
The force is investigating whether the batch is defective and warned members of the public to take extra care when handling any type of firework.
Inspector Gavin Russell, from Wishaw Police Office, said: "So far we have recovered several hundred but there could have been up to a thousand hidden there.
"We do not know who the fireworks belong to or indeed who owns the shed they were in.
"What concerns us is that they now appear to have got into the hands of local youngsters."
Anyone with information should contact Bellshill Police Office on 01698 202400 or Crimestoppers on 0800 555 111.