At least one weapon was discovered Thursday and sniffer dogs were brought in to aid in an extensive search of the area, The Local.se reported.
Police did not say what kind of weapons were found.
"We want to confirm that there are not more weapons in the area," Jimmy Modin of the the Malmo police told the Skanska Dagbladet newspaper. "For now, we are labeling this as an aggravated weapon crime."
No other details of the incident were given by police.
"We're not currently going out with any information regarding this case," Modin said.
The schools, one of which was a preschool, were expected to remain closed through the school day Friday. Students were alerted to the closures via text message
"We don't know much more than that the weapon was found yesterday, nor why the police are carrying such a thorough investigation," Susanne Sellbjer, receptionist at one of the closed schools, told the TT news agency.