The shooter who opened fire inside a Minneapolis sign company Thursday was among "several" people found dead inside the building, according to police officials who won't specify how many people were killed.

Police had previously said at least two people were killed and four were wounded, including three critically, during the afternoon shootings at Accent Signage Systems. But during a Thursday evening news conference, Minneapolis Police Deputy Chief Kris Arneson wouldn't confirm the numbers.

"We do have several victims inside that are dead," Arneson said. When pressed to say how many, she said she didn't know and that the investigation could take several days.

She released few other details, including the shooter's possible motive or gender, but said the person who fired the shots died inside the building from a self-inflicted gunshot wound. She said police did not fire at the shooter.

None of the victims' names has been released.

Hennepin County Medical Center was treating four patients from the scene Thursday night, including three men in critical condition, according to a hospital spokeswoman.

Someone from inside the building called 911 around 4:30 p.m. to report the shootings, police said. The first officers on the scene quickly began evacuating people from the business, which is nestled in a residential area on the city's north side, and closed off several blocks.

Dozens of squad cars and SWAT officers swarmed the neighborhood Thursday afternoon, and traffic was stopped on a nearby bridge along Penn Avenue, where officers had rifles drawn and pointed at the business and a park below.

By Thursday evening, police vehicles were still surrounding the business.

People from the neighborhood milled around but deputies kept them back.

Marques Jones, 18, of Minneapolis, said he was outside a building down the street having his high school senior pictures taken when he and his photographer heard gunfire that sounded close.

"We heard about four to five gunshots," Jones said. "We were shocked at what happened and we just looked at each other. We all just took off running to our vehicles."

According to Accent Signage Systems' website, the company makes interior signage and lists its founder as Reuven Rahamim. A phone messages left at the business was not immediately returned, and a woman who answered the phone at Rahamim's residential listing declined comment.

The company employed 28 people as of July, according to a feature on the business in Finance & Commerce, a local business publication. The paper reported that U.S. Under Secretary of Commerce Francisco Sanchez visited it in August in a trip focused on exporting, and praised the company for its innovation.

The company developed a patented technology for producing signs in Braille and had licensed out the technology to companies in 38 countries, the newspaper said.

Minneapolis Mayor R.T. Rybak said employees who were working when the shootings occurred were together and being cared for Thursday evening.

"We are deeply sorry about what has happened here," he said, calling the shootings "a horrible tragedy."

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Associated Press writers Doug Glass and Jeff Baenen in Minneapolis and Barbara Rodriguez in Chicago contributed to this report.