The blast occurred around lunchtime at the Kvarnbergsskolan in Huddinge, south of Stockholm.
"The explosion took place during a chemistry lesson. Something went wrong," police spokesman Albin Närverberg told The Local.
"We've had reports that around ten people were injured."
Police later confirmed that nine students and two teachers received minor injuries and were receiving treatment on the scene.
Zakarias Labidi, 13, was one of the students who received minor injuries in the blast.
"I didn't have much time to think, it was like a shock," he told the TT news agency.
The 13-year-old explained that a bottle was hurled into the room.
"It landed about two metres from our table, then a teacher came to pick it up and throw it away. Then, she noticed it was warm and then it exploded in her hand. Liquid went all over her and on some of the other students," he said.
Emergency services and police evacuated the school, which has around 600 students in grades seven through nine, directing the children to a nearby community and recreation centre.
Damage to the building is also thought to be limited and the risk for fire low.
"None of the injuries are burns. The fire department will go in to make sure everything is okay, but there doesn't appear to be a fire associated with the explosion," said Närverberg.
There have also been reports of several people feeling nauseous and having trouble breathing following the blast.
Emergency workers told the TT news agency the explosion involved a plastic bottle that contained some sort of liquid, but further details remain unknown.
According to the Huddinge municipality website, the school has been closed and parents have been urged to pick up their children.
In addition to the nine students injured in the blast, two other students have since shown signs of being affected by the incident and are now being examined by medical personnel.
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