Regional authorities said in a statement that 25 people had sustained minor injuries in the blast and that Linkoping University as well as other medical facilities in the area had been called into help care for those injured.
The police website said a bomb squad was on its way to the scene, where windows were broken in some buildings.
There have been several cases in recent years of explosives being used in suspected gang-related attacks in Sweden, and spokeswoman Asa Willsund said the police were looking into whether the blast was connected to local criminal groups. "We have blocked the area and are working on getting a picture of exactly what has happened".
Photos published by tabloid Aftonbladet showed two multi-storey buildings with shattered windows and wrecked balconies, with some damage to their roofs also visible. One of the buildings has five stories, while the other has four.
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"We started to get a large number of calls from people about a heavy explosion in central Linköping, on Hamngatan", said Björn Öberg at the police's management center.
Rescue personnel outside a block of flats that were hit by an explosion, in Linkoping, Sweden, Friday, June 7, 2019.
"So far we have been able to confirm that there are number of people with light injuries".
Police said that there were no plans to evacuate residents.
The Associated Press contributed to this article.