A 25-year-old Polish citizen drove into Krakow's Main Market Square on Saturday and opened fire at multiple stops with an automatic weapon, killing six people and injuring 15 others, according to AP reporting carried by PBS and WCTV.

The victims included four women and two men — at least three of the women were Polish and one of the dead was a U.K. citizen, with two victims still being identified.

Police said the attacker wore military-style fatigues and a bulletproof vest, kept firing even after being shot by officers, and was wounded, arrested and taken to hospital, where he underwent surgery.

Two police officers were seriously injured, and police commander Marek Boroń said five non-Poles were among the wounded.

Mass shootings are rare in Poland, which is why an attack of this scale in the country's second-largest city and a major tourist hub is so jarring.

Kacper Rekawek, a senior researcher at the International Center for Counterterrorism in The Hague, told PBS that the attacker's military gear, guns and overall look resembled other "extreme right lone actors" in Europe, and that "these kinds of attacks have become successful in Poland."

Interior Minister Marcin Kierwiński said the man held "very radical" and "ultranationalistic" views, and Poland's defense minister called the attack an act of terror. Investigators believe he acted alone.

Africanews reports that witness footage captures pedestrians fleeing for safety as shots ring out, with shattered windows, overturned café chairs, ambulances and a rescue helicopter circling overhead.

Prime Minister Donald Tusk said hours after the attack that authorities found the bodies of three of the suspect's close family members — two women and a man — inside his home in Ostrowiec Świętokrzyski, about 150 kilometers northeast of Krakow.

"We have the next acts of this tragedy," Tusk told reporters. Police spokesperson Katarzyna Cisło described the gunman's path as a "wild ride" around the square, which is why people were wounded at several locations, and said other weapons and ammunition were found in his car.

The attack has triggered immediate security responses: Warsaw mayor Rafał Trzaskowski announced increased measures including road barriers along the capital's old-town main streets, per PBS.

Krakow mayor Łukasz Gibała declared official mourning until Wednesday but vowed the city would stay open to visitors, saying "the square will belong to us again."

The tragedy follows three school attacks in Mazovia province in mid-October that left one person dead and many wounded, including children.

PBS reports it was not immediately clear whether the weapons used were legal, noting around 411,000 people hold gun permits in Poland and interest in gun ownership has been rising — a debate now likely to intensify.