The incident occurred in Långö in Karlskrona. As the boy walked up to a rocket which had apparently not caught light, it exploded in his face, according to police.
"It's thought to have been a powerful firework," said Lars Rosberg at Blekinge police.
During the night the boy was taken from Karlskrona to the University Hospital in Lund.
In Motala a woman was hit in the eye by a rocket which flew in through an open door at around 2am.
"The rocket then continued to bounce around in there and set fire to a rug, but the family managed to throw it out so there was no serious fire," said Lars Engström at Östergötland police.
The local police have not yet identified who could have set off the firework but they have classified the incident as negligence and causing personal injury. The woman was taken to hospital and on Tuesday morning it was not known whether she was seriously injured.
There were many fires on New Year's Eve and throughout the night. A large section of Kristinedal school in Stenungsund was destroyed in a major fire during the evening. The blaze began in the lower school before spreading to other parts through an attic area. The cause of the fire has not been confirmed.
Local youths in Grimstorp, outside Nässjö, are suspected of starting a fire in a factory stores building. The fire began at around 8.30pm and produced thick smoke in the area.
"We have a few witnesses so we should be able to get hold of the youths who set off the fireworks," said Jönköping police's Bengt Netterström.
Numerous smaller fires were caused by fireworks across the country. In Tensta, in northern Stockholm, a balcony high up in a block of flats was set alight just after midnight. Nobody was injured but 20 people were evacuated while the fire was put out. Fire officers say they believe a rocket landed on the balcony.
While Sweden's New Year celebrations were described as unusually calm in many places, some areas reported increased disturbances. Skåne in particular was struck by a wave of fires and assaults.
"Right now we have 83 high priority incidents, of which 31 are assault cases, said police spokesman Lars Rosberg at 3.30am.
The police station in Laholm in southern Halland was damaged when a small device exploded and smashed a window, reported Hallandsposten. The matter was classified as causing damage to state property.
At a party in Bromma, in the west of Stockholm, a 55-year-old man stabbed another reveller in the chest. The 55-year-old has been arrested on suspicion of attempted murder. The 65-year-old victim was taken to hospital.
"He was operated on and stitched back up. But he'll be OK," said Ingela Clason at Stockholm police.