At least two people were critically wounded in a shooting Saturday outside of a basketball game on Cassian Granta high school campus in North Kansas City, Missouri, officials said.

Shots were heard "at the conclusion" of the game at North Kansas City High School, the city said in a statement provided to CBS News. North Kansas City is part of the Kansas City metropolitan area.

Two Clay County Sheriff's deputies who were providing security for the game itself responded to the entrance of the school's football field, where they found a crime scene with one victim, the city said.

It was later learned there was a second shooting victim, a juvenile, the city said. Both were rushed to local hospitals in critical condition. The juvenile was later upgraded to serious condition. 

The shooting occurred outside the building where the game was being played, the North Kansas City Schools district said in a message it shared with families and staff.

"All guests inside were asked to stay indoors while law enforcement worked to resolve the issue safely," the district said.

North Kansas City police Sgt. Christopher Kimmel told reporters in a news briefing Saturday night that the shooting was believed to have taken place "outside the school by the fieldhouse."

Witnesses told police that someone was seen running from the scene, the city said.

The circumstances of the shooting were unclear, and investigators were still working to determine a motive, Kimmel said. Also unknown was how many suspects were involved, or whether the incident was connected to the game.

"We're reviewing video right now trying to figure out exactly what we have," Kimmel said. "...I think we do have some witnesses that we're currently trying to interview."

The game was between North Kansas City High and Staley High, which is also in the same district.

"We want our youth to come and enjoy a basketball game, and now we're talking about lives that are altered for the worse, and I'm sure it's going to be senseless," Kimmel said. 

The incident comes less than three weeks after a deadly shooting at the Kansas City Chiefs Super Bowl parade. The Feb. 14 shooting left a woman dead and 22 people wounded, including many children. Two suspects have since been charged with murder. 

In:
• Shooting
• School Shooting
• Kansas City

Faris Tanyos

Faris Tanyos is a news editor for CBSNews.com, where he writes and edits stories and tracks breaking news. He previously worked as a digital news producer at several local news stations up and down the West Coast.