The Bloomington Police Department tweeted shortly after 8:15 pm that police and emergency medical crews were on the scene of a shooting at the mall.
The lockdown lasted for about an hour before the mall tweeted that shoppers were being sent outside.
Police did not immediately provide details on whether anyone was injured or arrested.
Videos posted on social media show shoppers hiding in stores, and an announcement in the mall warned people to seek shelter.
Some videos show shoppers running for cover after a loud bang is heard. The reported shooting comes as shopping centres and malls across the US see an influx of customers just days before Christmas.
Emergency vehicles converged in the snowy parking lot outside and police could be seen putting up yellow crime scene tape near the Nordstrom store.
The Mall of America had asked shoppers to remain in “the closest secure location.”
Since it opened in 1992, the mall has been the largest in the US and is a tourist destination and community gathering spot.
It bans guns on the premises but does not have metal detectors at its entrances.
The mall was placed on lockdown in August after a reported shooting at the suburban Minneapolis shopping complex sent some shoppers running for cover and two people were wounded last New Year's Eve during an apparent altercation.
Representatives from the city of Bloomington and the Mall of America did not immediately return requests for comment.
