Four women and two men were killed in the mid-day attack in the sprawling plaza at the heart of Krakow's medieval Old Town, according to police. The assailant, a Polish national, fired from a vehicle moving through the square and was shot by officers at the scene, city officials said in a series of posts on X. He was taken to a hospital around 3 p.m. local time.

Katarzyna Cisło, a spokesperson for Krakow police, told the broadcaster TVN24 that the perpetrator wore military-style fatigues and used a military-type long gun. Officers later found numerous other weapons and ammunition in his car, she said.

Video circulating on social media showed what appeared to be an injured police officer firing at the suspect before dropping to his knees and rolling onto his back. The officer, who did not appear to have backup nearby, was seen struggling to reload his firearm and clutching his right arm. His condition was not immediately known. Małopolska Police said in a post on X that no officer had been killed, correcting what it called inaccurate reports.

Other footage from the scene showed a black sedan racing through the square as dozens of people fled in different directions at the sound of gunfire. Some clips depicted responders attempting life-saving measures on victims, with bodies visible on the streets after the attack.

Taylor Dorfmeister, who was in the square with his roommate when the shooting began, said there was a pause before the crowd reacted and then everyone ran. He took shelter inside a building.

"We ran up the stairs in the building to hide and it was a dead end, which is when I was the most terrified since the gunshots were [loud] and near," Dorfmeister told NBC News.

Polish Prime Minister Donald Tusk wrote on social media that police were working to establish the circumstances of the attack. U.S. Ambassador to Poland Tom Rose called it "a savage and murderous attack that's shattered the peace of Poland" and said America stands with the country.

The city announced a mourning period through Nov. 11. An earlier municipal post said investigators were still working to determine the full scale of the incident.

The Main Market Square, laid out in 1257, is considered the largest market square in Europe and is home to the historic Cloth Hall and St. Mary's Basilica. It is part of Krakow's Old Town, a UNESCO World Heritage Site, and has long served as the city's commercial and tourist center. The square's mansions once housed Polish royalty and aristocrats; during the Nazi occupation of World War II it was renamed for Adolf Hitler and used as a propaganda base.

Saturday's attack struck at the heart of a city whose historic center draws visitors from around the world and where the square functions as a civic gathering place. Authorities have not released a possible motive, and the investigation is ongoing.